The 10 year anniversary of the 9/11 attacks is being marked across the world on Sunday. However, the occasion is being discussed in significantly different ways - for some it is a time for mourning, for others a time for reflection or critique.
The series of coordinated terrorist attacks on New York, Washington and Pennsylvania on 11 September 2001 killed nearly 3000 people. Four passenger jets were hijacked by Al-Qaeda, two crashed into the Twin towers of the World Trade Centre in New York, one into the Pentagon in Washington and one into a field in Pennsylvania.
Images of the smouldering remains of New York's World Trade Centre, in particular, remain embedded in the public memory. Yet, with a wide range of approaches to such memories, it seems a summary is in order.
US President Barak Obama decided to travel to all three sites on Sunday.
Thousands are expected outside a village in south-western Pennsylvania for the dedication of stage one of a national memorial to those on United Airlines Flight 93 who foiled an apparent bid by Al-Qaeda hijackers to strike Washington.
George W. Bush, president at the time of the attacks, will make his third visit to the crash site since 9/11, along with Vice President Joe Biden and former president Bill Clinton.
President Obama on Saturday said the United States was stronger 10 years after the attacks and Americans would "carry on" despite continued threats against their safety. This statement comes amidst heightened security fears in the US as investigations continue into an intelligence report suggesting a car or truck bomb plot is planned for the anniversary
He also noted that Al-Qaeda's strength has been sapped by relentless US efforts in the decade since the tragedy.
"Thanks to the tireless efforts of our military personnel and our intelligence, law enforcement and homeland security professionals, there should be no doubt: today, America is stronger and Al-Qaeda is on the path to defeat," Obama said in his weekly radio and Internet address.
US forces killed former Al-Qaeda leader Osama bin Laden, considered the mastermind of the 11 September attacks, earlier this year. The president referred to bin Laden's death and said the democratic movements in Arab countries cast a shadow over Al-Qaeda's legacy.
The anniversary has also sparked criticism of the US, in both its foreign and domestic affairs.
The attacks were a trigger for the subsequent 'War on Terror' launched by the then-president, George W. Bush, in partnership with other states. In 2001, war was declared in Afghanistan, and later on Iraq in 2003.
According to a research project by Brown University's Watson Institute for International Studies, the United States has spent an additional $400 billion on security plus $1.3 trillion on the wars in Iraq and Afghanistan before counting interest on war debt and healthcare for veterans.
There has also been heavy international criticism of the imprisonment of suspected militants captured abroad at the US military base at Guantanamo Bay, Cuba.
The invasion of privacy is also unsettling, especially for Muslims and people of Middle Eastern descent who face discrimination and have been caught up in the security net.
"It's worse now than it was on 11 September 2002," Dawud Walid, head of the Michigan branch of the Council on American-Islamic Relations, said. "I don't see things being dramatically different five to seven years from now."
A service to commemorate the anniversary will be held in London at St Paul's Cathedral on Sunday. The service will remember the sacrifices made by members of the Fire Department during the rescue effort as well as all those who have been victims of terrorist attacks across the world in the last decade.
British Prime Minister David Cameron said on Friday that Britain and the United States have lost some of their moral authority through some measures they put in place after 9/11.
Some measures, such as the establishment of the Guantanamo Bay detention camp, had been a mistake, Cameron told Al-Jazeera television.
"We can certainly see with hindsight and in some ways at the time, mistakes were made in that we lost some of our moral authority, which is vital to keep when you're trying to make your case in the world," Cameron said.
This comes after a three-year inquiry said senior officers should have done more to prevent the 2003 death of hotel worker Baha Mousa and sustained attacks by British troops on nine other detainees in Iraq.
UN chief Ban Ki-moon has used the approaching anniversary of 9/11 to renew his call for a global counter-terrorism treaty, which has been thwarted for a decade amid arguments over what constitutes terrorism.
The UN has more than 13 separate treaties that cover terrorism, terror financing, hijacking and weapons of mass destruction, but he wants a global convention to unite all aspects of counter terrorism and provide new impetus to combat threats.
"Our goal is to have a comprehensive convention dealing with the whole of international terrorism," Ban told a briefing on a visit to Australia.
Ban, however, said last month's bombing of a UN building in Nigeria showed that threats remained, despite global efforts. The car bomb attack killed 23 people and injured 80.
"My position is that terrorism cannot be justified under any circumstances. For whatever justifications, this must be stopped," Ban said.