In the Mediterranean, the Navy’s regional commander postponed a scheduled port call in Naples, Italy, for a destroyer so that the ship would remain with a second destroyer in striking distance of Syria during the crisis. Pentagon officials said the decision did not reflect any specific orders from Washington, but both destroyers had on board Tomahawk cruise missiles, long-range weapons that probably would be among the first launched against targets in Syria should the president decide to take military action.

On Friday, the Russian government called on President Bashar al-Assad of Syria to allow United Nations investigators into the areas east of Damascus where the attack occurred. But American and foreign diplomats said Russia’s move did not reflect any shift in its backing of Mr. Assad or its resistance to punitive measures in the Security Council.

In a statement, Russia’s foreign ministry put the onus on Syria’s opposition forces to provide secure access to the site of the “reported incident.” A second statement suggested that the Russians believed the attack was actually a provocation by the rebels. It cited reports criticizing government troops that were posted on the Internet hours before the attack.

“More and more evidence emerges indicating that this criminal act had an openly provocative character,” Aleksandr K. Lukashevich, a spokesman for Russia’s foreign ministry, said in the statement. “The talk here is about a previously planned action.”

However, Mr. Lukashevich may have been confused by YouTube’s practice of time-stamping uploaded videos based on the time in its California headquarters, no matter the originating time zone. The attacks occurred early Wednesday in Syria, when it would still have been Tuesday in California for about eight more hours.

Mr. Lukashevich praised the Assad government for welcoming Carla del Ponte, a member of a United Nations commission on Syria who suggested in May that the rebels had used chemical weapons, and he accused the Syrian opposition of not cooperating with the investigation by United Nations experts.

The Syrian government did not comment on Friday.

On Friday CBS News, citing administration officials, reported that American intelligence agencies detected activity at locations known to be chemical weapons sites before Wednesday’s attack. The activity, these officials believe, may have been preparations for the assault.