LONDON (REUTERS) - The United States' decision to weigh military action against Syria and growing evidence that the government there was behind a chemical weapons attack prompted Russia to change its stance towards its Middle East ally, the British government said.

"The mounting evidence that they have used those weapons and the discussions, particularly in the United States, about whether to take military action, have produced a change in the Russian position," Britain's Foreign Secretary William Hague told parliament on Thursday.