WASHINGTON -- Russian Foreign Minister Igor Ivanov said Friday that there is a "very high probability" that the United States and Russia will sign a treaty reducing offensive nuclear arms during a May 23-26 summit, AFP reported.

"We proceed from the premise that there is a very high probability for that and we will do everything that we can to achieve that," Ivanov said after meeting with U.S. President George W. Bush at the White House.

"There are still outstanding issues" to resolve if Bush is to sign an accord when he meets with Russian President Vladimir Putin, U.S. Secretary of State Colin Powell said later after talks with Ivanov.

"But I think I can say that we're both encouraged by the progress that we made today," Powell told reporters. "I think it's going to be a very, very successful summit."

The accord would aim to build on an oral agreement between Bush and Putin to slash their nuclear arsenals from 6,000 warheads to between 1,700 and 2,200 over the next 10 years, officials said.

White House spokesman Are Fleischer said Bush was "hopeful" of narrowing differences with Russia, which has balked at Washington's plan to store -- rather than destroy -- the decommissioned warheads.

Fleischer told reporters both sides still had to resolve "a series of issues, some of which are legal."

"I have not delved into the specifics of each one of them, but any announcement of this type, any codification of this type has a lot of T's to be crossed and I's to be dotted. And that's what the lawyers and negotiators are working on now," the spokesman said.

Fleischer declined to say whether the accord would be a formal treaty, but Ivanov told reporters that Moscow believes the subject matter means that "A more appropriate form will be a treaty."