Russia on Friday hailed a new nuclear arms treaty with the United States, but warned that US missile defence plans could still derail the key objective of reducing nuclear weapons.

Russian Foreign Minister Sergei Lavrov made it clear that Moscow could back out if the United States went too far with its plans to counter missile attacks by setting up defences in eastern Europe.

"The presidents agreed that the new treaty marks the transfer of Russian-US cooperation to a higher level in the development of new strategic ties," the Kremlin said in a statement after the agreement was announced.

It also said the new treaty establishes a linkage between strategic weapons cuts and missile defence systems -- an apparent reference to US missile shield plans that have angered Moscow.

"The mutual linkage between strategic offensive and strategic defensive weapons will be fixed in a legally-binding manner" in the new treaty, the Kremlin statement said.

Lavrov told reporters, "The agreement was reached in conditions where both sides have corresponding levels of strategic offensive and defensive systems.

"Any change to these levels gives each country the right to decide the question of whether it will continue to take part in the process of further reductions of strategic arms."

Asked whether the new treaty imposed restrictions on US missile defence, Lavrov said it "does not ban anyone from making unilateral decisions."

He also said the Russian parliament would proceed with ratification of the treaty only in coordination with the US Senate, where opposition from conservative Republicans could kill the treaty.

"We no doubt proceed from the fact that the ratification process will be synchronised," Lavrov told reporters, in an indication that Russian lawmakers would not ratify the pact unless it cleared the US Senate too.

The new treaty is to be signed April 8 in Prague by US President Barack Obama and his Russian counterpart, Dmitry Medvedev.

It replaces the 1991 Strategic Arms Reduction Treaty (START), a cornerstone of Cold War-era arms control which expired in December.

Obama had made the effort to replace START a central element of his push to "reset" badly strained relations with Russia.

In a telephone call on Friday where the two presidents clinched the deal, Medvedev told Obama the two sides had achieved a "balance of interests" in the treaty after months of talks, Medvedev's spokeswoman said.

"The presidents thanked each other for cooperation," Kremlin spokeswoman Natalya Timakova told Russian news agencies, descibing the phone call.

"Medvedev noted that this treaty reflects the balance of interests of both countries," Timakova added.

The Kremlin confirmed a White House announcement that the signing of the treaty would take place in Prague, the city where Obama made his pledge last year to seek a world free of nuclear weapons.

Signed in 1991, START led to steep reductions in the US and Russian nuclear arsenals and imposed a series of verification measures to build trust between the two former Cold War foes.