WASHINGTON (Reuters) - President Barack Obama sought to rally Americans behind the war in Afghanistan on the eighth anniversary of the September 11 attacks on the United States, as opinion polls show faltering public support for the conflict.
"Let us renew our resolve against those who perpetrated this barbaric act and plot against us still," Obama said at a somber ceremony attended by about 500 people under rain-filled skies at the Pentagon.
"In pursuit of Al-Qaeda and its extremist allies we will never falter," he said, before laying a wreath at a memorial for those killed at the Pentagon on September 11, 2001.
On that day, American Airlines Flight 77 from Washington's Dulles International Airport smashed into the walls of the U.S. military headquarters, killing 125 people, along with the plane's 59 passengers and crew and the five hijackers.
Al-Qaeda hijackers took control of four passenger planes on September 11, crashing two into the World Trade Center in New York and a third into the Pentagon. A fourth, United Airlines Flight 93, crashed into a field in Pennsylvania after the passengers and crew tried to retake control of the plane.
In all, about 3,000 people were killed.
In New York, relatives of those who died in the World Trade Center attack took turns reading the names of the victims, adding personal remarks of remembrance for their loved ones, while flutists and violinists played solemn music.
The reading of the names took place in a small park across the street from the World Trade Center site, which is now a huge construction area where four skyscrapers and a national museum and memorial plaza are planned.
But as Americans mark this year's anniversary there is growing disquiet over the eight-year-old war in Afghanistan, which the United States invaded in response to the September 11 attacks to root out Al-Qaeda and topple their Taliban backers.
Opinion polls show waning public support for the war that George W. Bush launched as part of his global "war on terror" that came to define his presidency.
Obama, who has ordered the dispatch of 21,000 more U.S. troops as part of a new Afghanistan-Pakistan strategy targeting Al-Qaeda and its Taliban allies, has been trying to stiffen American support for a war that has been going badly for the United States and its NATO allies.
In a speech to military veterans last month, Obama called it a "war of necessity" and said those behind the September 11 attacks were plotting to kill more Americans.
The chief plotter of the September 11 attacks, Al-Qaeda leader Osama bin Laden, has never been found, and U.S. officials believe he is hiding in Pakistan's tribal areas bordering Afghanistan.
A record 44 U.S. soldiers died in Afghanistan in July and last month's Afghan presidential election was dogged by allegations of widespread fraud that analysts say could contribute to more violence.
The White House is in an internal debate over whether to further increase troop levels as the top U.S. military commander in Afghanistan is expected to ask for thousands more, a step that could face resistance from Obama's fellow Democrats in Congress.
The Democratic chairman of the Senate Armed Services Committee, Carl Levin, said on September 11 that the United States should focus on boosting Afghan troop levels before considering sending more troops.
The speaker of the House of Representatives, Nancy Pelosi, said a day earlier she did not think there was much support in Congress for increasing troop levels in Afghanistan.
Polls show Americans have become less concerned about terrorism, and in a Gallup Poll conducted in June, only 1 percent of respondents mentioned it as the most important problem facing the United States.
There is also soul-searching about the harsh interrogation techniques that the Bush administration sanctioned in the questioning of terrorism suspects after September 11.
A recent Gallup poll showed Americans evenly split on an inquiry ordered by Obama's attorney general, Eric Holder, into CIA interrogation abuses, including cases of waterboarding or simulated drowning and "walling," where a detainee's head was slammed against a wall.
Bush officials, including former Vice President Dick Cheney, a vocal critic of Obama's handling of terrorism, have denied that torture was used and have defended the interrogation practices as legal.
The edginess that remains after the September 11 attacks was shown on the eighth anniversary when the U.S. Coast Guard set off a security scare with a training exercise in the heart of the U.S. capital. The exercise took place on the Potomac River near the Pentagon, close to the time Obama was there.