Former prime minister Tony Blair expressed his "heartfelt gratitude" to President Barack Obama today for the military operation which killed Osama bin Laden.
In a statement, he said the operation showed that "those who commit acts of terror against the innocent will be brought to justice, however long it takes".
Mr Blair was prime minister at the time of both the 2001 and the 2005 attacks, which in many ways shaped his time in power.
He said: "My heartfelt gratitude to President Obama and to all of those who so brilliantly undertook and executed this operation.
"We should never forget 9/11 was also the worst ever terrorist attack against UK civilians, and our thoughts are with all those - American, British and from nations across the world - who lost their lives and with their loved ones who remain and who live with their loss.
"9/11 was an attack not just on the United States, but on all those who shared the best values of civilisation.
"The operation shows those who commit acts of terror against the innocent will be brought to justice, however long it takes.
"So this is a huge achievement in the fight against terrorism but we know the fight against the terrorism and the ideology that Bin Laden represents continues and is as urgent as ever."