A decade after 9/11, the day that changed so much for so many people, the world's leaders and citizens paused to reflect Sunday on terror attacks in the US that took nearly 3,000 lives of people from more than 90 countries.

In a reminder that threats remain, a Taliban suicide bomber killed two civilians and injured scores of US soldiers in eastern Afghanistan.

Untold millions around the world pored over the memories of shock, sadness and stupefaction where they saw televised images or heard of the attacks 10 years ago — or learned of a friend or relative who had died.

The mostly somber commemorations from Sydney to Spain stood out against pockets of protest and the resuscitation of controversial old claims that the US government itself was behind the attacks.

About 500 soldiers gathered at Bagram Air Field near the Afghan capital, Kabul, for a ceremony in front of a piece of World Trade Centre rubble. It was briefly interrupted by a reminder of war — when a fighter jet buzzed closely overhead.

At NATO's headquarters in Brussels, a French soldier played taps and the flags of 28 alliance states were lowered to half-staff as a tribute to the victims. About 130,000 NATO troops — two-thirds of them Americans — now serve in Afghanistan. More than 2,700 service members have died in that war.

AP