President Vladimir Putin on Thursday accused the United States of raising the risk of nuclear war by threatening to spurn a key arms control treaty and refusing to hold talks about another pact that expires soon.
The United States has threatened to pull out of the 1987 Intermediate-range Nuclear Forces Treaty (INF) which bans Moscow and Washington from stationing short and intermediate-range, land-based missiles in Europe.
Putin said the move, if it happened, would have unpredictable consequences.
"We are essentially witnessing the breakdown of the international arms control order and [the start of] an arms race," Putin told his annual news conference with hundreds of reporters.
"It's very hard to imagine how the situation will develop [if the U.S. quits the INF Treaty.] If these missiles appear in Europe what should we do? Of course, we'll have to ensure our own security."
Another U.S.-Russia treaty, the New START pact, which limits the number of deployed strategic nuclear warheads each side can have, expires in 2021. Putin said he was worried that Washington didn't appear to be interested in discussing its future.
"No talks on extending this are yet being held. Are the Americans not interested, do they not need them? Ok, we'll survive and will ensure our own security which we know how to do. But in general, this is very bad for humankind because it takes us closer to a dangerous threshold."
The Russian leader, who said Moscow had developed nuclear weapons which he believed gave it an edge over other countries, warned the threat of a nuclear conflict was growing as a result of the U.S. moves. He also cited the dangerous tendency of lowering the threshold for using nuclear weapons and the idea of using ballistic missiles with conventional warheads.
"If, God forbid, something like that were to happen, it would lead to the end of all civilisation and maybe also the planet," said Putin.
"I hope that humankind has enough common sense and sense of self-preservation not to take things to such extremes."
The annual event, Putin's 14th of its kind, is used by the Russian leader to burnish his leadership credentials and send messages to foreign allies and foes.
Putin won a landslide re-election victory in March, giving him six more years in power. That will take his political dominance of Russia to nearly a quarter of a century, until 2024, by which time he will be 71.
Though he faces no serious political threat for now, plans to sharply raise the pension age saw his approval rating fall to below 60 percent for the first time in five years according to a poll published by the Levada Centre last month.
Putin, 66, has been in power, either as president or prime minister, since 1999.