In response to Mrs. Clinton’s allegations, the Russian foreign minister, Sergey V. Lavrov, accused the United States of hypocrisy on Wednesday, saying it had supplied weapons that could be used against demonstrators in other countries in the region. Mr. Lavrov, during a visit to Iran, repeated Russia’s claim that it is not supplying Damascus with any weapons that could be used in a civil war.

“We are not providing Syria or any other place with things which can be used in struggle with peaceful demonstrators, unlike the United States, which regularly supplies such equipment to this region,” Mr. Lavrov said. He singled out a recent delivery to “one of the Persian Gulf states” — perhaps a reference to Bahrain. “But for some reason the Americans consider this completely normal.”

Syria has long been a staunch Russian ally and is home to Russia’s only naval base on the Mediterranean Sea. But American officials have warned the Russians that Mr. Assad’s exit is inevitable, and that if Russia wants to preserve its influence in Syria, it needs to be part of the effort to arrange a political transition. If Russia is viewed as complicit in the Assad government’s attack on its own people, these officials said, it would be shunned by any new Syrian government, as well as by the rest of the Arab world, which is increasingly appalled by the violence.

Mrs. Clinton underscored this point in remarks Wednesday after meeting with India’s foreign minister: “Russia says it wants peace and stability restored. It says it has no particular love lost for Assad. And it also claims to have vital interests in the region and relationships that it wants to continue to keep. They put all of that at risk if they do not move more constructively right now.”

Though Mrs. Clinton’s remarks about the helicopters came in answer to a question at a session sponsored by the Brookings Institution, they were part of a lengthy discussion of the West’s options in dealing with Syria and seemed anything but accidental.