Diplomats from the two biggest nuclear powers have been trying to prepare a new agreement on cutting atomic weapons before the landmark 1991 Strategic Arms Reduction Treaty expires on Saturday.

But Russian and U.S. sources said last week that the new deal was unlikely to be ready by Dec 5 and that they hoped an agreement would be sealed by the end of the year.

“Intensive work on preparations for the signing are coming to a close,” the Russian Foreign Ministry said in a statement.

U.S. President Barack Obama and Russian counterpart Dmitry Medvedev said in a joint statement on April 1 that they intended to find a replacement for the deal by the time START-1 expired.

The Kremlin and the White House say a new agreement will be evidence of a “reset” relations after the friction of recent years.

In July Obama and Medvedev agreed to cut the number of deployed nuclear weapons by around a third from current levels to 1,500-1,675 each.

After the cuts - which have to be made within seven years of a new treaty taking effect - the United States and Russia will still have enough firepower to destroy the world several times over.