Two airlines that fly from Moscow to the United States must check passengers and their carryon bags for bombs, according to a government order Wednesday, one week after suspected terrorists crashed two Russian planes.

"The U.S. has determined it's prudent to take additional security measures to increase the protection of flights between the U.S. and Russia until we have more information to assess the situation," said Amy von Walter, a spokeswoman for the Transportation Security Administration (search).

The airlines affected are Delta Air Lines and Aeroflot Russian Airlines, which fly to the United States four times a day from Sheremetyevo International Airport, a Homeland Security Department (search) official said. Aeroflot has direct flights from Moscow to New York, Seattle, Los Angeles and Washington, D.C. Delta offers daily flights between Moscow and New York.

The two planes that crashed on Aug. 25 after near-simultaneous explosions, killing all 90 people on board, had left Moscow's Domodedovo Airport on domestic flights. The planes belonged to the Russian airline Sibir and a small regional airline, Volga-Aviaexpress.

Delta and Aeroflot were ordered to conduct tests of all passengers and their bags for explosives using various technologies, von Walter said. The airlines also must conduct more thorough screening of all cargo put aboard passenger planes, she said.

Airlines must take additional security precautions around the aircraft when they are at the Moscow airport, and they must inspect the aircraft before passengers board, said a Homeland Security Department official who spoke on condition of anonymity.

Russian authorities are looking into the possibility that suicide bombers brought the planes down, and are seeking information about two Chechen women believed to have been aboard — one on each plane.

Rafi Ron (search), former head of security at Israel's Ben Gurion Airport and now a security consultant in Washington, said the U.S. government should not limit the stricter security for U.S.-bound planes from Moscow.

Like the commission that investigated the Sept. 11 attacks, Ron advocates better technology at airport checkpoints so more passengers can be inspected for explosives. Currently, metal detectors — both hand-held and walk-through — do not sense nonmetal bombs, and only those passengers selected for extra screening are checked for bombs in U.S. airports.