US President Barack Obama understands Moscow's concerns over his call for both countries to reduce their nuclear weapon stockpiles, Russia's foreign minister was reported as saying on Saturday.

Obama had told his Russian counterpart Vladimir Putin during their meeting at the G8 summit that he would call for the two countries to cut the number of their atomic weapons, Foreign Minister Sergei Lavrov said in a television interview published on Saturday.

"President Putin answered by reiterating our position that when examining this issue, it is essential to take into account all factors that influence strategic stability, without exception," Lavrov said.

These include missile defence, space weapons and non-nuclear strategic weapons, he said.

"President Obama said that he understands the necessity of taking all of these issues into account when discussing the next steps in reducing nuclear weapons," Lavrov said.

Russia also wants any talks on cuts to include other nuclear armed states.

In a speech in Berlin on Wednesday, Obama called for the two former Cold War foes to reduce their atomic weapons by up to a third, taking them each to the 1,000 weapon mark.

Although Putin did not react directly to Obama's proposal, he had earlier said that Russia would not let its nuclear deterrent be undermined.

He said that Russia is faced with a situation in which countries are developing offensive capabilities by building up mid-range missiles and sophisticated non-nuclear weapons, and while the United States has worked to reconfigure its missile shield, the project is still going ahead.

"We cannot allow the balance of the system of strategic deterrence to be disturbed or the effectiveness of our nuclear force to be decreased," Putin said.

The previous ground-breaking cut was agreed by the United States and Russia in 2010 as part of the Strategic Arms Reduction Treaty (START) that Obama signed together with then president Dmitry Medvedev.

The treaty restricts the former Cold War foes to a maximum of 1,550 deployed warheads each. It was one of the greatest legacies of Medvedev and Obama before Putin returned to the Kremlin last year for a third term.