The U.S. delegation has slowed down nuclear disarmament talks with Russia in Geneva in the past two days, Russian Foreign Minister Sergei Lavrov said on Thursday.

"We noticed that the U.S. negotiators had slowed down. They said they needed additional directives," Lavrov said at a press conference in Moscow.

He added that a successor pact to the Strategic Arms Reduction Treaty (START-1) that expired on Dec. 5 is unlikely to be signed in Copenhagen at the end of this week.

"This is unlikely to happen in Copenhagen, considering there is still a lot of purely technical work ahead," Lavrov said.

The foreign minister, however, said Moscow and Washington are approaching the goal as the negotiations are proceeding consistently.

"If the negotiators from both sides concentrate on fulfilling the presidents' instructions, we will achieve the agreement quite soon," he said.

Lavrov said two key principles should be adhered to in working out a new pact.

"First, we need to ensure that nuclear weapons are reduced as much as possible. Second, verification and control measures should correspond to the new treaty rather than the old one," he said.

New verification and control measures should be milder and less expensive, Lavrov said.

Russian President Dmitry Medvedev and his U.S. counterpart Barack Obama announced at their first meeting in April that the two countries would find a replacement for the START-1 by the end of this year.

Moscow and Washington have been in intense talks since July, with negotiations going on in Geneva this week. Officials on both sides previously voiced hope that the deal could be clinched before the year's end.

The START-1, signed in 1991 between the Soviet Union and the United States, obliged both sides to reduce their nuclear warheads to 6,000 and delivery vehicles to 1,600.

A follow-up agreement concluded in Moscow in 2002, known as the Moscow Treaty, envisioned cuts to 1,700-2,200 warheads by December 2012.

The new treaty's outline agreed by the presidents at a July summit in Moscow included slashing nuclear arsenals to 1,500-1,675 operational warheads and delivery vehicles to 500-1,000.