U.S. President George W. Bush has surprised officials in both Washington and Moscow by accepting President Vladimir Putin's invitation to an informal summit in Sochi in early April, sources in both capitals said.

"The invitation was sent some time ago, and Bush's acceptance is highly appreciated as a sign of his personal constructive attitude," a Kremlin source said Thursday.

The source, speaking on condition of anonymity because of the sensitivity of the issue, said "some members of the [Bush] administration, including those working in the field of international affairs, advised Bush not to hurry with an answer and not to accept the invitation," the source said. "We hope that this personal approach will continue."

Bush told foreign reporters in Washington on Wednesday that he would travel to Sochi to discuss the strategic relationship, "the crucial part of which is missile defense," according to a transcript posted on the White House web site.

Bush is expected to travel to Sochi on Saturday, April 5, and will return to Washington the next day.

The meeting is likely to be the last in office between the two leaders as Putin is to hand the presidency over to Dmitry Medvedev in May and Bush's second and final term ends in January.

Both White House and Kremlin officials said Bush would try to spell out their countries' relationship past the leadership changes in a joint document announced by U.S. Secretary of State Condoleezza Rice last week in Moscow.

"President Bush outlined a draft of that relationship in a recent letter to President Putin and a discussion of this will certainly take place in Sochi," Kremlin spokesman Dmitry Peskov said. He added that he could not say when the final document would be ready.

Bush's National Security Advisor, Stephen Hadley, said the meeting might be an opportunity to provide a strategic framework for the relationship, identify areas of cooperation, and resolve some outstanding issues.

He told reporters in Washington that this would be "so that the relationship is in good shape to be handed over to their two respective successors," Hadley told reporters in Washington, according to a transcript posted on the White House's web site.

No official word was out whether President-elect Dmitry Medvedev would be in Sochi, but a source close to the summit's organization merely said Thursday that Washington had shown strong interest in Medvedev's presence. "The Russian side is well aware of that," the source said.

Medvedev was traveling in Siberia on Thursday and calls to his spokespeople went unanswered.

Bush and Putin are likely to focus on security issues as both are scheduled to meet at the NATO summit, which kicks off in Romania's capital, Bucharest, on Wednesday.

Putin will join Bush at a session of the NATO Russia Council on Friday, after which Bush will make a dash to Croatia, one of three countries expected to gain NATO membership next week.

Hadley said Bush could be in Sochi after leaving Croatia later on Saturday, April 5, and before his return to Washington sometime Sunday, April 6.

Bush, who will be accompanied by his wife Laura, w ill leave Croatia's capital, Zagreb, that Saturday, Hadley told reporters in Washington.

"It is his intention is ... to try to go to Sochi after the stop in Croatia," he said, adding that details were still being worked out.

The State Department referred all inquiries about the visit to the White House. As of late Thursday, the White House press service had yet to reply to written requests for comment.

A hot topic of the summit will be the possibility of NATO expansion to include more former Soviet republics. Moscow heavily opposes Washington's plans to offer Ukraine and Georgia a closer relationship with the alliance, something that could ultimately lead to membership.

Bush will hold talks on this issue in Kiev on Monday and Tuesday.

It was also unclear whether Bush and Putin would go fishing in Sochi. "This depends on the working schedule of both Presidents, on the agreement and certainly on weather conditions," Peskov said. But he added that fishing in the Black Sea was fun.

Putin's invitation is believed to be a repayment of his trip to Bush's family home in Kennebunkport, Maine, last July, which included a deep-sea fishing trip.

At the Asia-Pacific Economic Cooperation summit in Sydney in September, Putin said he had invited Bush to go fishing "not only in the United States, but also somewhere in Siberia."

"I don't think that this time they will manage to get to Siberia," Peskov said.