Sen. Marco Rubio, R-Fla., and Rep. Tom Cotton, R-Ark., said the U.S. should provide military assistance to Ukraine unless Russia quickly withdraws its troops from Ukraine's Crimea region, but stopped short of calling for U.S. forces to become directly involved.
The freshmen lawmakers, members of their chambers' foreign relations committees, said that if Russia doesn't back down in the coming days, Ukraine "will require more than just our moral and financial support."
That includes "defense assistance in the form of a military assessment team to examine Ukraine's needs, as well as enhanced intelligence cooperation," the pair said in jointly written opinion piece for cnn.com.
In the meantime, they said the U.S. and its European allies must begin the process of punishing Russia with a trade embargo, "explore" restrictions on imports of Russian natural gas and cut off Russian banks from the international financial system.
The lawmakers also said the U.S. should send natural gas to its allies and partners in Eastern Europe to make them less susceptible to "Russia's efforts to use energy as a weapon."
Russian President Vladimir Putin "clearly decided that the benefits of an armed intervention in Ukraine outweighed whatever costs the United States would be willing to impose," they said. "The United States must reset that calculation."
The lawmakers added that the neighboring country of Georgia -- which Russia invaded in 2008 -- also should be supplied with anti-aircraft and anti-tank weapons, and they pressed for Georgian membership in NATO.
"Our allies and partners in Central and Eastern Europe are undoubtedly watching this situation with much apprehension about what it says about the credibility of American leadership and the future of the transatlantic alliance," they said. "To this end, we need to support our emerging partners in the region."
The two Republicans also said NATO should "review its force posture" in the region and take "tangible steps" to protect its members against Russian aggression. Ukraine isn't a NATO member. But fears persist that Russia could target next the Baltic nations of Estonia, Latvia and Lithuania -- NATO members that, like Ukraine, have significant Russian minorities.
"Some may argue that these [potential U.S.] actions are overly provocative and will only encourage Russia to be more aggressive," the lawmakers said. "If we do not take these steps, similar actions by Russia and other authoritarian regimes around the world will only proliferate."
The pair also criticized the Obama administration for last week proposing significant military cuts that are "entirely unrealistic in today's threat environment."