The White House cautioned Tuesday it would not "rush" a long-awaited new arms reduction treaty with Moscow, after Russian Foreign Minister Sergei Lavrov said the deal could be ready within three weeks.

Russian and US negotiators have been holding intensive talks to agree a new treaty to replace the 1991 Strategic Arms Reduction Treaty (START) that expired in December without a successor agreement in place.

The talks have been complicated by disagreements over a range of issues, including US plans for a missile defense system in eastern Europe.

White House spokesman Robert Gibbs said both sides were working through the last remaining sticking points in the way of agreeing a new treaty and that the US side hoped for a successful conclusion "in short order."

But Gibbs also appeared to hint that the Americans would not fast-track the process just to get a new deal signed before President Barack Obama's nuclear non-proliferation summit in Washington in April.

"If it takes, quite frankly, many more weeks past April to get something that we believe is in our best interest, then we're not looking to rush the negotiations," to allow time for a pre-summit signing ceremony, Gibbs said.

Earlier, as negotiations resumed in Geneva, Lavrov mentioned a more optimistic timeline.

"We want everything to be completed in the next two to three weeks. The chances are there," Lavrov was quoted as saying by Russian news agencies.

The broad outlines of a new START replacement treaty on nuclear weapons have been clear since a summit in July, when Obama and Russian President Dmitry Medvedev agreed to slash the number of warheads on either side to between 1,500 and 1,675.

The presidents also agreed that the number of weapon systems capable of delivering the warheads should be limited to between 500 and 1,100.

The United States has said it currently has some 2,200 nuclear warheads, while Russia is believed to have about 3,000.