President Bush and top European Union officials on Wednesday announced a series of agreements aimed at cracking down on terrorism and vowed to make sure Iran keeps its promise to halt development of nuclear weapons.

"We believe that strong ties between America and Europe are essential to peace and the prosperity of the world," Bush said at the White House briefing following the annual American-European summit (search).

He added that both the United States and the European Union are "threatened by global terror and we are determined to defeat it."

The president also demanded that European leaders block funding — whether from charities, individuals or other sources — to the Palestinian Islamic militant group Hamas (search).

A senior official of Palestinian leader Yasser Arafat's Fatah faction (search) said Wednesday that three militant groups had signed an agreement to halt attacks on Israelis for three months, a major step forward for the U.S.-backed peace plan. However, Hamas has not confirmed the deal and the Israelis have not commented on it.

"I'll believe it when I see it," Bush said when asked about the cease-fire. "It's one thing to make a verbal agreement. In order for there to be peace in the Middle East, we must see organizations such as Hamas dismantled."

Attorney General John Ashcroft and the Greek Minister of Justice, Philippos Petsalnikos, who was representing the European Union as a whole, signed extradition and mutual legal assistance agreements, which authorize joint investigative teams, video testimony in court cases and sharing information on suspect bank accounts.

The agreements will also help speed up the extradition of terrorists and expand the range of offenses that qualify for extradition.

"These treaties focus not on our differences, but on our common values," Ashcroft said.

The European Union and United States also strengthened export controls of dangerous materials designed to stop the proliferation of nuclear, chemical and biological weapons — measures aimed especially at the nuclear threats posed by North Korea and Iran.

Bush noted that the U.N.'s International Atomic Energy Agency (search) recently stated that Iran has failed to open up to weapons inspectors. Tehran has repeatedly said it does not have a nuclear-weapons development program.

Bush said Wednesday's agreements would also give the IAEA more tools to investigate what he called "clandestine" weapons activities.

"Iran has pledged not to produce nuclear weapons, and the entire international community must hold that regime to its commitments," Bush said.

One main, if unspoken, objective of the U.S.-EU summit was to rebuild long-standing ties strained by disagreements over the Anglo-American invasion of Iraq.

But Greek Prime Minister Costas Simitis, whose country currently holds the rotating six-month presidency of the EU, said reports of the strain were exaggerated.

"The transatlantic relationship works, does produce results and is important to all of us," he said. "A transatlantic relationship is essential to a national order."

European Commission President Romano Prodi acknowledged that the U.S. and some of its traditional allies differed over the Iraq war, but said that discussion of the differences would be fruitless.

"The differences are shrinking," Prodi said. "When Europe and the United States are united, no problem and no enemy can stand against us — this is the real lesson."

For its part, the EU delegation told the Americans it considered weapons of mass destruction a major global threat — something U.S. officials had complained the Europeans were not taking seriously.

But there are other issues besides Iraq that divide the United States and the Europeans.

Europe has stuck by its 1998 moratorium on the import of genetically modified foods, which many European consumers fear as health risks. Bush has scolded the EU in recent weeks, charging that it is worsening famine in Africa by discouraging African nations from investing in biotechnology.

The moratorium costs American farmers an estimated $300 million a year in lost exports alone, and the U.S. plans to take the dispute to the World Trade Organization.

The two sides also announced their intention to enter negotiations on a common U.S.-European Union aviation market — a single "open skies" agreement (search) to lift restrictions on airline destinations and replace bilateral agreements now in place.

The European Union delegation included Simitis, Prodi and foreign policy coordinator Javier Solana. They met with Bush, Vice President Dick Cheney, national security adviser Condoleezza Rice, Secretary of State Colin Powell and other Cabinet members.

Greek government spokesman Christos Protopapas said the Europeans hoped the summit would "constitute the starting point for a new era in the strategic partnership between the United States and Europe after the tension that existed in recent months."

Fox News' Liza Porteus and The Associated Press contributed to this report.