U.S. President Barack Obama is urging Russia to negotiate with members of the World Trade Organization to resolve the remaining issues blocking it from becoming the 154th member of the group.

The White House said that Russian President Dmitry Medvedev called President Obama Wednesday to wish him a happy birthday, a day ahead of his 50th birthday on Thursday. White House spokesman Jay Carney said the two leaders discussed Russia's 18-year quest to join the WTO, with Mr. Obama stressing that Russia needs to finish talks on its membership so that it can join the WTO by the end of the year.

Carney said the two leaders agreed that “significant progress” on Russia joining the WTO had been made since the two leaders talked a few weeks ago. One issue yet to be resolved centers on objections by foreign automakers that they commit to major production in Russia if they want lower import fees for car parts.

Mr. Obama also spoke with Russian reporters, telling them that the new nuclear disarmament treaty between Russia and the United States is an example of “tremendous progress” made in bilateral ties. Mr. Obama noted that when he was born during the Cold War, no one would have imagined that Washington and Moscow would be partners on the international stage.

He called Mr. Medvedev a “strong patriot” who fiercely defends his country's interests, but also recognizes that Russia will prosper from further bilateral and multilateral engagement. Mr. Obama said Mr. Medvedev is widely respected for holding those views.

Russia has released a postage stamp, matching envelope, and postmark in honor of Mr. Obama's birthday.

President Obama is traveling to his hometown of Chicago later Wednesday for events that include a gala fundraiser celebrating his birthday.