UNITED NATIONS — The U.N. Security Council has imposed sanctions on two Iranian companies 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 on Thursday.

U.S. U.N. Ambassador Susan Rice 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.