Iraq's leaders, including the president and prime minister, have repeatedly called on Iran to release two U.S. hikers convicted by Tehran for spying, Foreign Minister Hoshyar Zebari told Agence France Presse on Friday.

"We passed messages to the Iranians at all levels, from the president himself to the prime minister to the foreign minister," Zebari said, referring to President Jalal Talabani and Prime Minister Nouri al-Maliki.

The United States on Thursday urged Americans to make immediate plans to leave Syria, which has been wracked by anti-regime protests for months, warning anti-foreigner sentiment is mounting.

"The U.S. Department of State urges U.S. citizens in Syria to depart immediately while commercial transportation is available," the State Department said in an updated travel warning.

Al-Qaida's chief of operations in Pakistan Abu Hafs al-Shahri has been killed, a senior U.S. official said Thursday, revealing the latest blow to the terror group's senior leadership.

The death of Abu Hafs in a Pakistani tribal district follows the killing of al-Qaida's number two Atiyah Abdul Rahman last month, and comes amid stepped up U.S. drone strikes following the killing of Osama bin Laden in May.

The United States said Wednesday it hoped the U.N. atomic agency would "very soon" give more detail on new information the watchdog has on possible military dimensions to Iran's nuclear program.

"The real fear is that Iran is continuing ... and has over many years continued to explore and to develop technologies with no applications other than in the military sphere," Glyn Davies, U.S. envoy to the International Atomic Energy Agency (IAEA), told reporters.

Tears flowed and bells tolled at Ground Zero as Americans marked the 10th anniversary of the 9/11 attacks in a rare moment of unity for a country still shaken by the horrific terror strikes.

President Barack Obama and his predecessor and political foe George W. Bush stood together in New York for the main ceremony at the site of the destroyed Twin Towers.

President Barack Obama vowed Saturday that the United States will not waver in its fight against terrorism, as his predecessor said Americans will "never forget" 9/11 and the heroes who helped defend the country.

With the world marking a decade since the deadliest attack on U.S. soil, and the tragedy seared into America's collective memory, communities across America honored those lost in the disaster, while New York and Washington beefed up police presence and Obama called for a "heightened state of vigilance" as Americans readied for the 10th anniversary under the shadow of a terror threat.

Major U.S. cities were on high alert Saturday as the nation began marking the poignant 10th anniversary of the September 11, 2001 attacks amid warnings of a new Al-Qaida linked terror threat.

Although details of the new suspected plot possibly involving car bombs in New York and Washington were sketchy, a U.S. official told AFP the threat was credible and somewhere between "aspirational" and a "boom."

A Pakistani citizen on Friday plead guilty to illegally attempting to export nuclear material to organizations in his homeland that are classed "of concern" to U.S. national security, justice officials said.

Nadeem Akhtar, 46, faces up to five years in jail and a $250,000 fine, for conducting a scheme to provide restricted items to clients in Pakistan, including agencies of the government in Islamabad.

The United States said Thursday it will veto a bid for U.N. recognition of a Palestinian state if it comes to a vote before the U.N. Security Council.

State Department spokeswoman Victoria Nuland said U.S. opposition to such a move by the Palestinians "should not come as a shock."

Sudan told U.S. officials of its desire to normalize ties with Israel, a leaked diplomatic cable said, in a potentially embarrassing revelation for one of the Jewish state's more outspoken critics.

Mustafa Osman Ismail, a senior adviser to President Omar al-Bashir, said one aspect of proposed cooperation with the United States included normalizing Sudan's relations with Israel, according to a cable published by WikiLeaks.