U.S. President Barack Obama said on Friday the United States and Russia are "quite close to an agreement" on further nuclear arms reduction after meeting his Russian counterpart Dmitry Medvedev in Copenhagen.

"We've been making excellent progress. We are quite close to an agreement," Obama told reporters after the meeting, which came on the sidelines of UN climate talks here. He said he was confident the deal will be completed "in a timely fashion."

The Russian president said only some technical details require "further work."

The United States and Russia are trying to find a replacement for the Strategic Arms Reduction Treaty (START-1) by the end of this year. The treaty, signed in 1991 between the Soviet Union and the United States, obliged both sides to reduce the number of their nuclear warheads to 6,000 and delivery vehicles to 1,600.

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