Russia dismissed U.S. criticism of its parliamentary election as unacceptable, urging to refrain from such "hostile attacks" in future.

Washington said it was seriously concerned by the conduct of election, in which Prime Minister Vladimir Putin's ruling United Russia party suffered a decline in support but won a slim majority in the lower house.

U.S. Secretary of State Hillary Clinton, who has been seeking to consolidate improvements in the sometimes strained relationship with Russia, suggested earlier on Tuesday, Dec 6 the vote was neither free nor fair.

Thousands of Russians protested in Moscow against the alleged vote-rigging on Monday and demanded an end to Putin's rule. A few hundred stages similar protests on Tuesday.

"Regrettably, Washington sticks to outdated stereotypes and labels without even attempting to understand what is happening in our electorate," the Foreign Ministry statement said, describing comments by the White House, Clinton and the State Department as "unacceptable," Reuters reported.