The new US negotiator on a major arms reduction treaty with Russia said Tuesday that talks could last beyond a year-end target, pledging to seek the best possible deal.

President Barack Obama, who has vowed to work to a world without nuclear weapons, agreed last week with his Russian counterpart Dmitry Medvedev to jumpstart negotiations on a new treaty.

The 1991 Strategic Arms Reduction Treaty, or START, expires at the end of the year. Negotiated with the Soviet Union, it eliminated 80 percent of strategic US and Russian nuclear weapons from Europe.

"We need to keep our eye on the prize over the next six months," said Rose Gottemoeller, the new assistant secretary of state for verification and compliance, who will be in charge of negotiations on START''s successor.

But she added: "If things aren''t going well, you can''t rush to the finish just to get something done."

"I want to make it clear that from the perspective of the United States, we will do what we have to do to get this negotiation done," she told a conference at the Carnegie Institute for International Peace.

But she noted that Secretary of State Hillary Clinton had also said that "if necessary, we will look for ways to find more time for the negotiators."

Obama pledged with Medvedev -- who called him "my new comrade" -- to set in motion diplomacy for further big cuts in nuclear weapons. In a major speech in Prague, Obama also called for a world where the ultra-destructive weapons are abolished.

Sergei Kislyak, the Russian ambassador to the United States, voiced willingness to work with Obama to abolish uclear weapons but said it would be a "difficult task."