The United States and Russia are currently in an active phase of drafting a new pact to replace the Strategic Arms Reduction Treaty (START 1), a spokesman for the U.S. Department of State said.

START 1, signed in 1991 and due to expire on December 5, is the bilateral basis for Moscow and Washington''s nuclear disarmament and the two countries began another round of talks on the issue in Geneva on Monday.

"We have very intensive negotiations going on. We do not want to negotiate in public. We are taking the tasking from our two presidents very seriously, the Russian side and the American side," Ian Kelly told the daily press briefing in Washington.

Russian President Dmitry Medvedev and his U.S. counterpart Barack Obama agreed in July in Moscow on the outline of a deal to replace START 1, including cutting their countries'' nuclear arsenals to 1,500-1,675 operational warheads and delivery vehicles to 500-1,000.

The drafting of the new pact was one of the key themes of talks held in Moscow during last week''s visit of U.S. Secretary of State Hillary Clinton, and the negotiating teams worked on specific language during meetings in Geneva earlier this month.

The Russian delegation in Geneva this week is headed by Anatoly Antonov, director of the Foreign Ministry''s Department of Security and Disarmament, while the U.S. team of negotiators is led by Assistant Secretary of State Rose Gottemoeller.