Vladimir Putin on Sunday said the United States would have to cut 755 diplomatic staff in Russia and warned of a prolonged gridlock in its ties after the US Congress backed new sanctions against the Kremlin.

The Russian president added bluntly that Russia was able to raise the stakes with America even further, although he hoped this would be unnecessary.

A US state department official denounced the move as a "regrettable and uncalled for act," adding that Washington was now weighing a potential response.

On Friday, the Russian foreign ministry demanded Washington cut its diplomatic presence in Russia by September 1 to 455 people - the same number Moscow has in the US.