BAGHDAD (AP) -- Al-Qaida is rebuilding in Iraq and has set up training camps for insurgents in the nation's western deserts as the extremist group seizes on regional instability and government security failures to regain strength, officials say.

Iraq has seen a jump in al-Qaida attacks over the last 10 weeks, and officials believe most of the fighters are former prisoners who have either escaped from jail or were released by Iraqi authorities for lack of evidence after the U.S. military withdrawal last December. Many are said to be Saudi or from Sunni-dominated Gulf states.

During the war and its aftermath, U.S. forces, joined by allied Sunni groups and later by Iraqi counterterror forces, managed to beat back al-Qaida's Iraqi branch.

But now, Iraqi and U.S. officials say, the insurgent group has more than doubled in numbers from a year ago -- from about 1,000 to 2,500 fighters. And it is carrying out an average of 140 attacks each week across Iraq, up from 75 attacks each week earlier this year, according to Pentagon data.

"AQI is coming back," U.S. Sen. Lindsey Graham, a Republican from South Carolina, declared in an interview last month while visiting Baghdad.

The new growth of al-Qaida in Iraq, also known as the Islamic State of Iraq, is not entirely unexpected. Last November, the top U.S. military official in Iraq, Army Gen. Lloyd Austin, predicted "turbulence" ahead for Iraq's security forces. But he doubted Iraq would return to the days of widespread fighting between Shiite militias and Sunni insurgents, including al-Qaida, that brought the Islamic country to the brink of civil war.

While there's no sign of Iraq headed back toward sectarian warfare -- mostly because Shiite militias are not retaliating to their deadly attacks -- al-Qaida's revival is terrifying to ordinary Iraqis.

Generally, the militant group does not does not launch attacks or otherwise operate beyond Iraq's borders. For years, it has targeted Shiite pilgrims, security forces, officials in the Shiite-led government and -- until it left -- the U.S. military. On Tuesday, a series of bombings and drive-by shootings killed six people, including three soldiers and a judge, in Baghdad and the former al-Qaida strongholds of Mosul and Tal Afar in northern Iraq.

Each round of bombings and shootings the terror group unleashes across the country, sometimes killing dozens on a single day, fuels simmering public resentment toward the government, which has unable to curb the violence. And the rise of Sunni extremists who aim to overthrow a Shiite-linked government in neighboring Syria has brought a new level of anxiety to Iraqis who fear the same thing could happen in Baghdad.

"Nobody here believes the government's claims that al-Qaida is weak and living its last days in Iraq," said Fuad Ali, 41, a Shiite who works for the government.

"Al-Qaida is much stronger than what the Iraqi officials are imagining," Ali said. "The terrorist group is able to launch big attacks and free its members from Iraqi prisons, and this indicates that al-Qaida is stronger than our security forces. The government has failed to stop the increasing number of victims who were killed since the start of this year."

In the vast desert of western Iraq near the Syrian border, security forces have discovered the remnants of recent insurgent training camps, said Lt. Gen. Ali Ghaidan, commander of the army's ground forces. An army raid last month on Iraq's sprawling al-Jazeera region, which spans three provinces, found a 10-tent campsite littered with thousands of bullet shell casings, Ghaidan told The Associated Press in an interview.

"This indicates that this place has been used as a shooting range to train terrorists," said Ghaidan, one of the highest ranking officials in the Iraqi army.

Two DVDs found in the al-Jazeera raid show mounted anti-aircraft machine guns. Forty gunmen shout "God is great" at a shooting range that a subtitle locates in Iraq's western Anbar province. Separate footage shows pickup trucks with Anbar license plates. The AP obtained copies of two DVDs, which Iraqi officials believe were filmed in the first three months of this year.

"Al-Qaida leaders decided that al-Jazeera is the best area to train their fighters because it is very hard for security forces to reach it," said Shiite lawmaker Hakim al-Zamili, who sits on parliament's security and defense committee and has been briefed on the camps.

Intelligence indicates as many as 2,500 al-Qaida fighters are now living in five training camps in the al-Jazeera area, according to two other senior Iraqi security officials. The officials, who spoke on condition of anonymity because they were not authorized to release the information, estimated that only 700 al-Qaida fighters were in Iraq when U.S. troops withdrew. Six months earlier, in June 2011, U.S. Defense Secretary Leon Panetta told the U.S. Senate that 1,000 al-Qaida remained in Iraq.

Earlier this summer, al-Qaida in Iraq launched a campaign dubbed "Breaking the Walls," which aimed at retaking strongholds from which it was driven by the American military. Sabah al-Nuaman, spokesman for the government's counterterror services, acknowledged that Iraqi forces have struggled to contain al-Qaida since the U.S. military's departure.

Iraqi and U.S. officials agree that Iraqi forces have improved their ability to gain terrorism intelligence from informants and prisoners. But they still struggle to intercept technical communications like al-Qaida's cell phone calls, radio signals and Internet messages -- one of the methods used by the U.S. military.

"The Iraqi efforts to combat terrorists groups have been negatively affected by the U.S. pullout, but we are trying our best to compensate and develop our own capabilities," al-Nuaman said.

The U.S. withdrew its military as required under a 2008 security agreement negotiated during the White House administration of then-President George W. Bush.

President Barack Obama considered leaving several thousand troops in Iraq past the 2011 withdrawal deadline. But negotiations disintegrated last fall when Baghdad refused to extend legal immunities to any U.S. combat troops remaining in Iraq, meaning they could have been prosecuted for defending themselves if under attack.

Republicans blame Obama, a Democrat, for failing to push Baghdad harder or to find a compromise that would have let U.S. troops remain in Iraq as a safeguard against al-Qaida and deteriorating Mideast stability. On Monday, GOP presidential candidate Mitt Romney accused the White House of wasting gains the U.S. made in Iraq.

Obama pushed back Monday, saying he had fulfilled a campaign promise to end the Iraq war.

"Gov. Romney said it was tragic to end the war in Iraq. I disagree," Obama said in a campaign speech. "We cannot afford to go back to a foreign policy that gets us into wars with no plan to end them."

There now are about 260 active-duty troops and civilian Defense Department employees who have diplomatic immunity to remain in Iraq to train security forces on military equipment that Baghdad bought from the United States. Among them are 28 U.S. special operations forces who have been training Iraqi counterterror soldiers in the capital. But the money for their posts runs out at the end of the year unless Congress agrees to restore their funding.

The two senior Iraqi security officials said al-Qaida fighters have been easily moving between Iraq and Syria in recent months to help Sunni rebels overthrow Syrian President Bashar Assad, whose Alawite religious sect is an offshoot of Shiite Islam. And in Anbar province, some fighters linked to al-Qaida have regrouped under the name of the Free Iraqi Army -- an attempt to align themselves with the rebels' Free Syrian Army.

Anbar tribal sheikh Hamid al-Hayes, a retired security official who helped U.S. forces fight al-Qaida in Anbar at the height of the insurgency, said the Free Iraqi Army is recruiting fighters and planning to overthrow the Shiite-led government in Baghdad. "They want to mimic the Syrian revolution," he said. Al-Nauman, the counterterror spokesman, denied that and said the group is merely a subset of al-Qaida fighters who adopted the new name to "attract the support of the Iraqi Sunnis by making use of the strife going on in Syria."

Al-Qaida in Iraq for years had a hot-and-cold relationship with the global terror network's leadership. It was the Syrian civil war, now in its 19th month, that prompted global al-Qaida leader Ayman al-Zawahri last February to embrace the Iraqi insurgency in hopes of recruiting fighters and support against Assad.

Before that, in 2007, Zawahri and Osama bin Laden distanced themselves from the Iraqi militants for killing civilians instead of only targeting the U.S. military and other Western targets. Now, there's little doubt that Zawahri's appeal to al-Qaida in Iraq bolstered its legitimacy and injected confidence into the insurgency just as the U.S. troops left.

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Associated Press Writers Sameer N. Yacoub in Baghdad and Ken Thomas in Washington contributed to this report. Follow Lara Jakes on Twitter at: https://twitter.com/larajakesAP