Swedish police in the southwestern city of Gothenburg have arrested four people suspected of preparing a terror attack, Swedish media said Sunday quoting intelligence reports.

"Four people suspected of preparing a terror attack" were arrested late Saturday, said TT news agency quoting Sara Kvarnstroem, spokesman of the Saepo intelligence agency.

Russian President Dmitry Medvedev on Sunday ordered his government Sunday to shut down unreliable airlines after 43 people were killed in a chartered plane crash that wiped out a top hockey team.

The decision came as the nation mourned the latest in a string of deadly air accidents that earlier saw Medvedev request the removal from operations of Russia's older Soviet-era jets.

A Taliban suicide bomber driving a truck attacked an advance NATO combat post in central Afghanistan, wounding 89 people including 50 American soldiers, the U.S. Army said Sunday.

News of Saturday's attack came as the world marked the 10th anniversary of the 9/11 attacks that killed almost 3,000 people in the United States and led to the invasion of Afghanistan and toppling at the end of 2001 of the Taliban.

The United States is considering a request from Turkey to base Predator drones there to operate against Kurdish separatists based in northern Iraq, The Washington Post reported late Saturday.

Citing unnamed senior U.S. military officials, the newspaper said a decision to deploy the drones could strengthen the U.S.-Turkish diplomatic alliance but draw the United States deeper into the conflict.

State police explosives experts gave an all-clear Saturday after investigating a "suspicious item" that forced gate evacuations at Dulles airport near Washington on the eve of 9/11 anniversary events, a spokesman told Agence France Presse.

A item was detected around 4:30 pm (20:30 GMT), and an area around a cargo container on an airfield was evacuated, said Dulles International Airport spokesman Robert Yingling.

Guinea Bissau Prime Minister Carlos Gomes Junior said Saturday Libya's ousted leader Moammar Gadhafi would be welcomed "with open arms" if he seeks exile in the west African country.

"The Libyan guide Moammar Gadhafi deserves all the respect of our government who will host him with open arms. He will be welcome in our country, if he needs exile in our country," Gomes Junior told the independent Radio Bombolom.

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.

Fresh overnight attacks killed at least 15 people in Nigeria, the latest in a wave of recent killings in an area beset by sectarian violence, a local government official said Saturday.

"Fifteen people were killed ... in Vwang district of Jos south local government area of Plateau state in a midnight attack," a government spokesman Pam Ayuba said.

An Iranian warplane crashed on Saturday in the northwestern city of Tabriz without causing casualties, as the Islamic republic conducts military maneuvers in the area, media reports said.

"An Iranian warplane crashed this morning in Tabriz," the English-language network Press TV reported, adding that the pilot was able to parachute to safety before impact.

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."