Russia's foreign minister and the US secretary of state, in negotiations over a deal to slash their countries' nuclear arsenals, pledged Tuesday to respect the treaty's broad outlines, the Russian foreign ministry said.

Sergei Lavrov and Hillary Clinton said it was necessary to "coordinate the work by (Russian and US) delegations in Geneva" that have been going on for six months, the ministry statement said.

In a phone conversation initiated by Washington, Lavrov and Clinton stressed the need to do this with "strict respect for the broad outlines agreed on by the presidents" Dimitry Medvedev and Barack Obama in July.

Negotiations on a replacement to the 1991 Strategic Arms Reduction Treaty (START), which expired on December 5, have dragged on for months despite periodic reports that the two sides were near agreement.

The broad outlines of a new treaty on nuclear weapons have been clear since a summit in July, when Obama and 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 carriers capable of delivering the warheads should be limited to between 500 and 1,100.