Tight security in force around the world

Tight security was being enforced across Europe last night, even though officials reported no specific threats. "Now, we always have to consider the unthinkable," said the Belgian Interior minister, Antoine Duquesne.

In Germany, police detained a Syrian-born man for questioning on suspicion that his clothing business was a front for smuggling in Islamic militants and that he had contacts with the Hamburg-based terror cell behind last year's attacks. Prosecutors said they were questioning the man, his wife and their two sons.

"The suspected contacts were with both the living and the dead from the Hamburg group," an intelligence source said. Three of the four hijackers, including the ringleader Mohammed Atta, were part of the Hamburg cell.

The French Transport minister, Gilles de Robien, said of the increased security: "We cannot be insensitive to the anniversary of this event."

The prosecutor who led the probe into Osama bin Laden's operations in Italy said the new threat to Europe in the aftermath of 11 September came from "freelance" terrorists who had no direct connections to al-Qa'ida.

Meanwhile, the United States shut four of its embassies in Asia after receiving specific threats of planned attacks by al-Qa'ida bombers. At the same time, law enforcement agencies around the world increased security after the most precise warnings received in recent days focused on targets outside the US.

Washington closed the embassies – in Malaysia, Indonesia, the Philippines and Cambodia – after receiving "specific and credible threats". The State Department issued a worldwide caution, urging Americans to be especially vigilant. "There is a continuing threat of terrorist actions, which may target civilians and include suicide operations," the department said.

"[The US continues to receive] credible indications that extremist groups and individuals are planning additional terrorist actions against US interests. Attacks on places of worship and schools, and the murder of American citizens demonstrate that as security is increased at official US facilities, terrorists and their sympathisers will seek softer targets," it said.

Ralph Boyce, the US ambassador in Jakarta, said his mission had been closed until further notice. "We know that the al-Qa'ida network is still far from defeated. We received another graphic example of that in just the past few hours with the news about ... the specific terrorist threat against our embassy," he said.

In Malaysia, the US embassy was also closed until further notice and the embassy in Cambodia for three days, with officials citing similarly "specific and credible threats". In the Philippines, the embassy was placed under a security "lock-down".

Around two dozen US diplomatic posts around the world were temporarily closed to public business. American military forces in Bahrain were put on the highest alert. The headquarters of the US Fifth Fleet are in Bahrain and about 4,000 sailors and other troops are based there.

The US Navy issued a warning to shippers following unconfirmed reports that al-Qa'ida may be planning attacks on oil tankers.

"While the US Navy has no specific details on the timing or means of the planned attacks, and there are no indications than an attack is imminent, the threat should be regarded seriously," the Navy said.