UNITED NATIONS (AP) — The U.N. Security Council imposed sanctions on two Iranian companies Thursday for smuggling arms to Syria and other countries.

The council's committee monitoring an arms embargo and other sanctions against Iran added cargo airline Yas Air and SAD Import Export Company to its blacklist.

Susan Rice, the U.S. ambassador to the U.N., welcomed the new designations, saying the companies were responsible for shipping ammunition, assault rifles, machine guns, mortar shells and other arms from Iran to Syria.

"The committee's decision underscores the growing international concern over Iran's use of the transportation and shipping sectors as a means to export arms and conduct other illicit activities in violation of U.N. sanctions," she said.

The U.N. has imposed four rounds of increasingly tougher sanctions on Iran over its nuclear program. The U.S. and its Western allies believe Iran is trying to build nuclear weapons but Tehran insists its nuclear program is purely peaceful.

Rice said Thursday's sanctions add to those already imposed by the council on Iran's transportation sector "to further erode Iran's ability to exploit transportation and shipping means for its illicit uses."

"It is incumbent on all states to redouble their efforts to detect, prevent, inspect, and seize any Iranian arms shipments, whether by land, sea or air," she said in a statement.