In New York yesterday, two floors of the United nations building were evacuated when two more letter bombs addressed to Al-Hayat, the newspaper targeted in the London attack, were discovered.
Two security guards were hurt by the London postal booby trap. Three other devices, believed to contain Semtex which were also sent to Al-Hayat, were destroyed in controlled explosions by anti-terrorist officers.
At the beginning of the year, five letter bombs, disguised as Christmas cards, were sent to Al-Hayat's Washington office in the United States, although none exploded.
The US booby traps, which are being investigated by the FBI, were sent from Alexandria in Egypt. Staff at Al-Hayat, a respected publication, said that the letters sent to the London offices also came from Alexandria. There is concern that there may be further terrorist devices still in the post.
During yesterday morning's explosion, Barry Roach, 46, from west London, suffered serious facial and abdominal injuries, and Andy McKenzie, 35, from south-west London, suffered from shock and burst ear drums, but was later released from hospital. The letter exploded in the basement post- room in the six-storey office block in Hammersmith.
Jihad Khazen, editor of Al Hayat said the attack had come without warning. He said security had been stepped up in the wake of the attacks in the US. "Since that here we have installed a scanning machine," he said. He added that the letter had tripped off a warning signal in the machine.
"It made a noise going through the machine, he carried it in his hands and it blew up," he said. "We don't know if the guard opened it or what happened. There's no danger to his life, we hope his eyes are not affected."
He added: "We would like to know which party we provoked. We have been criticising extremism in the Arab world for the last eight years.
"I hope and pray there will be no more attacks. We will not change. We will maintain our moderate position on Arab and international affairs."
Susannah Tarbush, a reporter on the newspaper, added: "We are always receiving threatening phone calls because of the nature of politics in the Arab world."
Al-Hayat, is a daily newspaper, printed in Arabic, that is owned by the Prince Khalid Bin Sultan, a member of the Saudi Arabian royal family. It sells 165,000 copies daily, mainly in the Middle East and particularly in the Gulf states. Most of the staff are Lebanese.
The newspaper adopts a moderate line on most issues - refusing to support Islamic terrorist acts - and has angered a wide variety of militant groups with some of its comment articles. Among those known to be unhappy with the paper are the various Islamic fundamentalist groups challenging goverments all over the Arab world.
FBI officers are reported to by investigating links between the Washington devices and the 1993 bombing of the World Trade Centre and a foiled plot to attack other New York landmarks. Four militant Muslims were jailed for life for the World Trade bombing. Alternatively the attack may be a strike against the Saudi royal family.