WASHINGTON — The U.S. military, backed by the firepower of the aircraft carrier USS Theodore Roosevelt, continued Tuesday to shadow a convoy of Iranian cargo ships in waters off the coast of war-torn Yemen.

The key concern: the ships could hold weapons intended for the Iranian-supported Houthi rebels, violating United Nations resolutions.

The Iranian ships remain in international waters off of Yemen, Army Col. Steve Warren, a Pentagon spokesman, said Tuesday. It consists of nine cargo vessels. There are no warships in the Iranian convoy.

The Roosevelt, with 5,000 sailors and 60 aircraft, is monitoring the ships. The Navy has several other ships off Yemen, including the USS Normandy, a guided-missile cruiser.

“We are continuing to watch this Iranian convoy,” Warren said.

He maintained that the deteriorating security situation in Yemen and the threat to safe seas was the primary reason for the Roosevelt’s move from the Persian Gulf toward Yemen on Sunday and Monday. Warplanes from the Roosevelt had been conducting airstrikes against ISIL terrorists.

Strikes against ISIL targets in Iraq and Syria continue despite the Roosevelt’s absence, Warren said. The U.S.-led coalition in that fight includes Air Force fighters and bombers as well as warplanes from American allies in the Middle East and Europe.

White House spokesman Josh Earnest said the carrier’s deployment was meant to help assure “freedom of navigation” and the “free flow of commerce” in the region.

He declined to discuss concerns about Iran shipping weapons to rebels in Yemen, or whether the United States gave a heads up to Tehran.

“I don’t have any communications with the Iranians to convey to you at this point,” Earnest said.

He noted that the new deployments “augment” the existing U.S. military presence in the area.

Earnest repeatedly declined to say how the United States might deal with an Iranian ship but added that the administration has often raised concerns about Iranian support for the rebels.