Obama Pays Solemn Tribute at Ground Zero: We Will Never Forget

U.S. President Barack Obama paid solemn tribute at the site of the downed Twin Towers, days after 9/11 architect Osama bin Laden was shot dead by American commandos in his Pakistani lair.

Intel found in bin Laden's compound revealed al-Qaida was considering a possible train attack at an unspecified location in the United States as a grim marker of this year's 10th anniversary of the September 11 attacks.

U.S. officials played down any imminent threat, describing the plot as "aspirational", but it did perhaps indicate that bin Laden remained more integral to the everyday running of al-Qaida than previously thought.

In a moment of high symbolism in New York, Obama laid a wreath at Ground Zero before hugging relatives of those killed when al-Qaeida extremists, presumed to be acting on bin Laden's orders, plowed their hijacked planes into the World Trade Center and the Pentagon.

Obama, making his first visit to Ground Zero as president, did not make a speech, but solemnly bowed his head and observed a moment of silence after laying the wreath along with city officials.

He spoke earlier at a firehouse that lost 15 men battling the infernos on 9/11, issuing a stark message to America's enemies around the world.

"When we say we will never forget, we mean what we say," he said.

Obama is to visit Fort Campbell in Kentucky on Friday to meet some of the elite commandos, said to be from a renowned naval squad known as "Team Six", who sneaked into Pakistan in stealth helicopters and took out bin Laden in the dead of night.

The president "will have the opportunity to privately thank some of the special operators involved in the operation," a U.S. official said on condition of anonymity.

In Pakistan, where Islamists have significant popular support, the largest religious political party Jamaat-e-Islami called for protests across the country on Friday to denounce the killing of the al-Qaida leader.

Hundreds of people took to the streets in the insurgency-riven city of Quetta near the Afghan border to pay homage to the slain extremist and call for holy war against America.

The crowd shouted "Long live Osama" and torched a U.S. flag, while Abdul Qadir Looni -- a senior figure in an Islamist party -- told the rally: "Osama's services for Muslims will be remembered forever".

"He challenged the greatest Satan and usurper like America and awakened Muslims across the globe. This gathering pays tribute to him."

But reaction from the Muslim world to bin Laden's death has so far been muted, in what analysts say is a sign the al-Qaida founder has lost popularity, particularly among Arab youth who have turned to popular protest.

Pakistan's police and army again barred world media from reaching bin Laden's house in Abbottabad -- a leafy garrison town two hours' drive from the capital -- on Friday, setting up checkpoints and deploying reinforcements.

"The presence of media was a hurdle in the investigation. There were also some security threats, so we sealed the neighborhood again," district police chief Mohammad Kareem Khan told Agence France Presse.

In the Bilal Town suburb where the sprawling villa was located, people have spraypainted on walls: "Osama bin Laden Town".