U.S. presidential candidate Barack Obama has called on Iran to accept a European proposal to halt its nuclear activities. Obama, who has been meeting in Paris with French President Nicolas Sarkozy, called the standoff with Iran extremely serious. Lisa Bryant has more from Paris.

Democratic presidential contender Sen. Barack Obama (r), greets French president Nicolas Sarkozy, at the Elysee Palace in Paris, 25 July 2008

Barack Obama's remarks came as he is winding up a world tour that has taken him to Afghanistan, the Middle East and Germany. He spoke at a joint news conference with President Sarkozy in Paris, following talks between the two that touched on Afghanistan, Iraq and climate change, among other issues.

On Iran, Obama said the international community must send a clear message to Tehran regarding its nuclear program, which the Iranian government insists is for purely peaceful purposes. He urged Iran to accept proposals to freeze its uranium enrichment program, which the U.S. and European Union fear is part of a secret effort to build nuclear weapons.

"My expectation is that we're going to present a clear choice to Iran: change your behavior and you will be fully integrated into the international community with all the benefits that go with that. Continue your illicit nuclear program and the international community as a whole will ratchet up pressure with stronger and increased sanctions. And we should have no illusion that progress will come easily," he said.

Iran has been given two weeks to answer to a demand by world powers that it suspend its uranium enrichment activities following a meeting in Geneva last weekend.

Obama also said again that Afghanistan was a war the international community had to win.

The democratic presidential hopeful has been given an enthusiastic welcome during his European stops. He spoke before an estimated crowd of 200,000 people in Berlin, Thursday, an unprecedented turnout for a U.S. presidential candidate abroad.

In an interview printed in Le Figaro newspaper Friday, President Sarkozy called Obama "his buddy" and said he had always believed Obama would win the Democratic primaries. After Paris, Obama next travels to London where he wraps up his international trip.