As Londoners went to work on Friday morning, stopping to lay flowers at the site of the July 7, 2005, attacks, the mood was one of unease mixed with resignation and defiance.

"I was there. It could have been me, so I am just lucky to be alive and remembering those who weren't that lucky," said Robert Andrews, 29, who was on one of the bombed London Underground trains.

"I am aware it could happen again but I am not worried," he told Reuters. "I have just got to get on with my life."

In what appeared to be a well-timed bid to fuel fears, a video surfaced on Thursday apparently showing one bomber, Shehzad Tanweer, reading his last statement before death.

The previously unseen video, broadcast on Qatar-based Al Jazeera television, also showed al Qaeda's deputy leader Ayman al-Zawahri, suggesting a link between
Osama bin Laden's network and the bombers.

NO ONE CHARGED

The failure of the police to charge anyone in connection with the attacks, despite an exhaustive inquiry, has added to unease.

The British government says it knows little about the motivation of the bombers, their possible training abroad or their alleged links to al Qaeda.

A survey by the Pew Global Attitudes Project released in Washington on Thursday showed 42 percent of Britons were very concerned about a rise in Islamic extremism in Britain compared to 34 percent a year ago.

Many of Britain's 1.8 million Muslims feel their community has been unfairly targeted by the police since the attacks. Two botched anti-terrorist operations in which police shot two innocent men, killing one of them, have not helped.

Survivors of the bombings say an official report into the attacks published in May did not answer all their questions. Many want a full public inquiry into the events which, like the September 11 attacks in the United States, have become etched into the British psyche as a simple date -- 7/7.

British Prime Minister Tony Blair, whose decision to send troops to Iraq and Afghanistan was cited by Tanweer, and some commentators, as a reason for the bombings, will try to shift attention away from such criticism when he joins the nation in observing a 2-minute silence at midday (1100 GMT).

At 8:50 a.m. and at 9:47 a.m. -- the times the bombs went off -- candles of remembrance were lit under the vast dome of St Paul's Cathedral as a single bell tolled.

Commemorative plaques were to be unveiled close to where the bombs went off later in the day.

The Daily News said authorities in Beirut, at the request of U.S. officials, arrested one of the suspected conspirators, identified as Amir Andalousli, in recent months and that agents were seeking other suspects around the world.

The newspaper said the FBI and New York police officials declined comment on the investigation, which it quoted a source as describing as "ongoing."

The Daily News quoted a counterterrorism source as saying officials were alarmed because the plotters allegedly got a pledge of financial and tactical support from Jordanian associates of Abu Musab al-Zarqawi, the leader of al Qaeda in Iraq before he was killed last month in a U.S. air strike. The paper said it was not clear if any cash or assistance was delivered.

Lebanon's government had been asked by the United States to hold off on announcing the arrest while operations to disrupt the plot were continuing, the Daily News quoted sources as saying.

It said New York officials, according to sources, believed the plan could conceivably work with enough explosives placed in the middle of the tunnel.

But it added that some experts did not consider the plan feasible because the tunnel was protected by concrete and cast-iron steel and that even if the tunnel cracked, the Wall Street district would not flood because it was above the level of the river.

Seven men were charged in the United States last month with conspiring to blow up the landmark Sears Tower in Chicago and FBI buildings in Miami and four other cities as part of a pledge to al Qaeda to wage war against America. U.S. officials said the plot never went beyond the earliest stages.

Instead, they believe a complicated mix of factors is behind the outpouring: a desire to show that al Qaeda is still potent; a new sophistication in the use of propaganda, and finally, sheer coincidence as several different messages have all surfaced within a short time span.

U.S. officials and terrorism experts said they take al Qaeda's threats seriously. The two men are believed to be hiding somewhere in the hostile, tribal border area between Pakistan and Afghanistan.

Bin Laden was not heard from for a year prior to January 2006. But he and Zawahri have now issued 11 audio and video tapes this year, the highest frequency recorded since the September 11 attacks, analysts say.

"They are trying to prove that the movement's not dead," said Kenneth Katzman, a terrorism analyst at the Congressional Research Service, the in-house think tank of Congress.

The two leaders may have felt they had to respond quickly to last month's U.S. military success in killing Abu Musab al-Zarqawi, the leader of al Qaeda in Iraq.

A failed U.S. attempt to kill Zawahri in January and possible greater ease of movement for al Qaeda leaders in Pakistan's northwest frontier region might have also contributed to the higher volume of tapes, Katzman said.

Ben Venzke, head of intelligence company IntelCenter whose clients include the U.S. government, said the back-to-back timing of the messages did not mean they were actually designed to produce a threatening crescendo.

"Does this correlate to any kind of future attacks? I think it doesn't lend itself to an easy yes or no," he said, although certain elements of past messages such as references to U.S. territory could indicate an increased likelihood of a future attack.

Venzke saw some of the tapes as a quick al Qaeda response to major events, such as the death of Zarqawi. Others were more general commentaries on current events which were issued when they were ready. Still others were anniversary features issued to mark the date of a past attack.

GROWING MEDIA SAVVY

In part, experts traced the recent wave of messages to al Qaeda's increasing media savvy and better logistics.

"It's a result of their ongoing propaganda efforts which have become even more sophisticated," a U.S. counterterrorism official said. "It demonstrates that they've greased the wheels. They've gotten better at this with time."

Coupled with its growing production expertise, al Qaeda leaders have increasingly felt compelled to reassure followers after setbacks while claiming credit for events that seem favorable to their cause.

"Bin Laden and Zawahri are trying to piggy-back on events they consider favorable, such as the Taliban resurgence, the upsurge of Islamic militants in Pakistan, the takeover by the Islamic Courts Union in Somalia. By coming out with this many videos, they are trying to give the impression that 'this is because of us,"' Katzman said.

Gen. Russ Howard, an Army terrorism expert who retired last year, said al Qaeda might be trying to debunk U.S. assertions that the organization was losing central control of its supporters to local or "homegrown" Islamic militants who operate independently.

"This may be a bit of propaganda asserting that there is some type of central control -- that maybe we have this all wrong," Howard said. "It may be a way of telling those franchise groups or wannabe groups that al Qaeda is still in the game, even despite the killing of Zarqawi."