President Vladimir Putin said Tuesday that Russia will boost its nuclear arsenal by more than 40 intercontinental missiles this year, in a move likely to further unnerve the West.

The declaration from the Kremlin strongman came as Russia reacted with fury to reports that the U.S. is planning to bulk up its military deployments in eastern Europe, with tensions between Russia and the West are at their highest since the end of the Cold War over the conflict in Ukraine.

U.S. Secretary of State John Kerry on Monday pressed his Russian counterpart Sergei Lavrov to ensure that Moscow respects the ceasefire in eastern Ukraine, the State Department said.

In a telephone call to Lavrov, Kerry "urged Russia to seize the opportunity of upcoming meetings of the Trilateral Contact Group and its Working Groups to accelerate progress on implementing the Minsk agreements," signed in February, said John Kirby, a State Department spokesman.

A journalist who published the first reports from Edward Snowden's leaked documents offered a detailed rebuttal Monday to allegations that Russian and Chinese spies accessed the former intelligence contractor's files.

Glenn Greenwald, writing on online news website The Intercept, said the reports by the Sunday Times and BBC were based on the false premise that Snowden kept possession of the files he took from the US National Security Agency.

Nuclear armed states continue to upgrade their stockpiles despite an international trend towards disarmament, the Stockholm International Peace Research Institute reported Monday. 

Between 2010 and 2015 the number of warheads fell from 22,600 to 15,850 according to the institute's annual disarmament report which said the U.S. and Russia represented the bulk of the reduction.

Poland said on Sunday it is in talks with the United States on the possibility of Washington storing heavy weaponry on Polish soil, as regional tensions run high over Russia and the conflict in Ukraine.

Defense Minister Tomasz Siemoniak said the negotiations were part of discussions on increasing the American military presence in Poland and other eastern European members of NATO.

Ukraine's faltering peace deal suffered fresh setbacks on Saturday when Kiev reported the deaths of six soldiers and accused Moscow of abetting an attack on one of its Russian consulates.

The latest fatalities in the twisting and hotly disputed zone separating Ukrainian forces from their pro-Russian foes in the separatist east add to the strains of a February truce designed to end one of Europe's deadliest conflicts in decades.

Britain has been forced to remove some of its spies after Russia and China accessed the top-secret raft of documents taken by former U.S. intelligence contractor Edward Snowden, British media reported.

The BBC and the Sunday Times cited senior government and intelligence officials as saying agents had been pulled, with the newspaper saying the move came after Russia was able to decrypt more than one million files.

The Pentagon is "poised" to station heavy weapons for up to 5,000 American troops in several Eastern European and Baltic countries to deter Russian aggression, The New York Times reported Saturday.

The proposal, if approved, would be the first time since the end of the Cold War that the U.S. has had heavy military equipment -- including battle tanks -- in newer NATO members that were once under Moscow's influence as part of the Soviet Union.

Ukraine's faltering peace agreement suffered fresh setbacks Saturday when Kiev reported the death of six soldiers and accused Moscow of abetting an attack on one of its Russian consulates.

The latest fatalities in the twisting and hotly disputed zone separating Ukrainian forces from their pro-Russian foes in the separatist east add to the strains of a February truce deal designed to end one of Europe's deadliest conflicts in decades.

Russian President Vladimir Putin on Saturday met Turkish counterpart Recep Tayyip Erdogan for talks expected to touch on energy issues and the Syria crisis.

The two leaders met a day after attending the opening ceremony of the inaugural European Games, hosted by Azerbaijan and tainted by controversy over the ex-Soviet country's rights record.