LONDON (Reuters) - Police launched an anti-terrorism advertising campaign on Monday, encouraging people visiting or living in London to report any suspicious behaviour they might see in the capital.

The country has been on high alert since four Britons killed 52 people on London's transport system in July 2005 in Western Europe's first Islamist suicide bombings.

London police's anti-terrorism chief Peter Clarke said the five-week press and radio campaign had not been launched in response to any specific threat, though the threat of attack remained real.

"We want people to look out for the unusual -- some activity or behaviour which strikes them as not quite right and out of place in their normal day to day lives," he said in a statement.

"Terrorists live within our communities, making their plans whilst doing everything they can to blend in, and trying not to raise suspicions about their activities."

The campaign is designed to raise awareness of what terrorists might need or use to plot an attack.

"Terrorists have a lot of work to do before they attack," Clarke added. "They need money and may commit cheque, credit card and identity fraud to finance their activities.

"They also need transport to move around in and they may raise questions over where they are going by being vague about their movements."