US President George W Bush has officially announced that the US will withdraw from the 1972 Anti-Ballistic Missile treaty with Russia.

This step was not a surprise for us. However, we consider it a mistake

Russian President Vladimir Putin said that the move was not unexpected but that he considered it a "mistake".

Both Mr Bush and Mr Putin said that the decision would not undermine Russian national security.

Russia warning

"Defending the American people is my highest priority as commander in chief and I cannot and will not allow the United States to remain in a treaty that prevents us from developing effective defences," Mr Bush said at the White House Rose Garden.

He had informed Congressional leaders of his decision on Wednesday.

Earlier on Thursday, the US ambassador in Moscow delivered a formal document informing the Russian Government of the decision and invoking Article 15 of the treaty, which gives Russia six months' notice before the treaty expires.

"This step was not a surprise for us. However, we consider it a mistake," Mr Putin said in a national television broadcast.