LONDON (AFP) - - London marked the third anniversary Monday of the suicide bombings on the city's transport network, with ceremonies at blast sites as survivors and the victims' families remembered the deadly attacks.

A total of 56 people were killed, the four bombers included, in the July 7, 2005 blasts that tore through three London Underground trains and a bus at the height of the morning rush hour.

London Mayor Boris Johnson, the government's London minister Tessa Jowell and transport chiefs were among those who laid flowers outside King's Cross railway station at 8:50 am (0750 GMT).

Johnson's tribute on his wreath read: "We honour the memory of those who died on 7/7 2005, we salute the courage of those who were injured and our thoughts and prayers are with all victims and their families."

The event was exactly three years on from when three bombs ripped through the Tube trains at the height of the morning rush hour.

Survivors and families of the 52 victims visited the three Underground stations -- Russell Square, Aldgate and Edgware Road -- where the bombs went off, and Tavistock Square, where another home-made bomb later wrecked a double-decker bus.

Compared to the first anniversary in 2006, subsequent anniversaries of the attacks have been low-key. Twelve months after the bombings, there was a national two-minute silence and a day-long memorial programme.

Dozens of the victims' families and some of the 700 who were injured are still waiting for compensation payments.

The attacks, perpetrated by four British Muslims, threw the spotlight on the threat from homegrown extremism, and the extent of opposition to Britain's foreign policy in Iraq and Afghanistan among the country's 1.6-million-strong Muslim community.

Three years on, Britain is still facing a "severe" threat from terrorism -- the highest level -- according to the security services, with increasingly frequent arrests of suspects under anti-terrorism legislation.

Last year, Jonathan Evans, the head of the domestic intelligence service MI5, said the number of people with suspected links to extremists in Britain had risen from 1,600 in 2006 to at least 2,000.

The government is currently pushing through parliament proposals to increase the pre-charge detention limits for suspected extremists from the current 28 days to 42 days, despite widespread outrage from civil liberties groups.

Britain's multi-cultural model, once held up as an example, has also come under scrutiny, with some suggesting Islamist sentiment is increasing, due in part to segregation and alienation among younger British Muslims.

In a television documentary looking at whether fear of terrorism had fuelled violence and intolerance towards British Muslims, international development minister Shahid Malik said many felt "like the Jews of Europe".

Malik -- Britain's first Muslim minister -- said he was not comparing Muslims' experiences to what Jews experienced during the Holocaust in Nazi Germany.

But in comments due to be broadcast later Monday, Malik said: "In the way that it was legitimate almost -- and still is in some parts -- to target Jews, many Muslims would say that we feel the exact same way.

"Somehow there's a message out there that it's OK to target people as long as it's Muslims. And you don't have to worry about the facts, and people will turn a blind eye."

An ICM survey for the documentary suggested that 51 percent of Britons blame Islam to some degree for the bombings while eight out of 10 Muslims believed their faith had faced more prejudice since then.