Tensions flared over plans to build a mosque near ground zero as rival demonstrations took place after family members of the victims of the September 11, 2001 attacks recited loved ones' names through tears at a sombre ceremony marking the ninth anniversary of the terrorist attacks on the US

After yesterday's official ceremony, around 2,000 activists rallied about five blocks from the site of the 2001 attacks to support the proposed Islamic community centre.

About 1,500 mosque opponents gathered nearby, chanting "USA, USA" and "No mosque here".

In an annual tradition, two bright blue beams of light rose from lower Manhattan in memory of the fallen towers on Saturday night.

Speaking at the Pentagon, where 184 people died on September 11, 2001, President Barack Obama alluded to the controversy over the mosque - and a Florida pastor's threat, later rescinded, to burn copies of the Koran, the Muslim holy book.

Mr Obama rejected the terrorists' efforts to spark conflicts among faiths.

"They may seek to exploit our freedoms, but we will not sacrifice the liberties we cherish or hunker down behind walls of suspicion and mistrust. They may wish to drive us apart, but we will not give in to their hatred and prejudice," Mr Obama said.

"As Americans we are not - and never will be - at war with Islam," the president said. "It was not a religion that attacked us that September day - it was al Qaida, a sorry band of men which perverts religion."

Family members gathering at observances in New York and Pennsylvania brought flowers, pictures of loved ones and American flags, but no signs of opposition or support for the mosque. As they read victims' names, they urged a restrained tone.

"Let today never, ever be a national holiday. Let it not be a celebration," said Karen Carroll, who lost her brother, firefighter Thomas Kuveikis. "It's a day to be sombre; it's a day to reflect on all those thousands of people that died for us in the United States."