Russia must take into account Syria's problematic nuclear stance before considering  cooperation with Damascus over nuclear power, a top United States official said Wednesday.

The comments followed reports that Russian President Dmitry Medvedev and his Syrian counterpart Bashar Assad had discussed the possibility of nuclear collaboration in Damascus earlier this week.

"Cooperation [with Syria] on atomic energy could get a second wind," Medvedev told reporters on Tuesday,  but provided no further details on what form the collaboration might take.

Russian news agencies quoted Assad as saying that he had discussed with Medvedev the possibility of building power plants, including nuclear ones, in Syria.

In September 2007 Israeli warplanes bombed a site in eastern Syria, which the U.S. later claimed was a nuclear installation aimed at building an atomic bomb with aid from North Korea.

Syria is a signatory to the international Non-Proliferation Treaty, which forbid member states from seeking nuclear weapons, while Russia is one of a handful of states permitted nuclear arms under the treaty.

On Wednesday, U.S. State Department spokesman Philip J. Crowley told reporters that Washington was cautious over any nuclear deal that included Syria.

Asked whether the United States approved of a possible nuclear bond between Russia and Syria, Crowley said that NPT signatories, including Russia, had "special responsibilities".

"All members have rights, but all members also have responsibilities," he said.

He added: "What concerns us is Syria has not answered questions that have been raised about its compliance with the NPT and all countries that contemplate energy cooperation need to take that into account," Crowley said.