Bomb Targets U.S. Mission in Libya's Benghazi BENGHAZI, Libya (Reuters) - A bomb exploded outside the U.S. diplomatic mission in the Libyan city of Benghazi overnight, an attack that could be retaliation for the killing, in a U.S. drone strike, of al Qaeda's Libyan second-in-command. An improvised explosive device went off on the roadside outside the gate of the mission, in an upmarket area of central Benghazi, but no one was injured, said an official at the U.S. embassy in the Libyan capital, Tripoli. Hours before the attack, Washington had confirmed that a U.S.-operated drone had killed Abu Yahya al-Libi, a Libyan-born cleric and senior al Qaeda operative, in Pakistan. U.S. diplomats said after the Benghazi blast they had asked the Libyan authorities to step up security at U.S. facilities in the country, where last year Muammar Gaddafi was overthrown in an uprising supported by NATO air power. A trade mission from the United States was scheduled to arrive in Libya for meetings starting on Thursday in Tripoli and Benghazi. It was not clear if these would now go ahead. "The possibility that this act took place because of what happened to Abu Yahya is, in my personal opinion, a very strong one," said Noman Benotman, a Libyan former Islamist who is now an expert on militant groups. He said there were several possible scenarios, but one was that the attack was carried out by militants connected to al Qaeda's north African arm. "Al Qaeda loyalists maybe wanted to deliver a message to the U.S. ...to say enough is enough," Benotman said. Libya's government made no immediate comment on the attack. The bombing will revive concerns about the lack of security in Libya, where the weak authorities are still struggling to restore stability after last year's revolt and where arms and explosives are easily available. In the past two months, there have been armed attacks on the offices of the Red Cross in Benghazi and on a convoy carrying the head of the United Nations mission to Libya. Tuesday's attack was the first time a U.S. facility had been targeted since Gaddafi was overthrown. "We have asked the Libyan government to increase its security around U.S. facilities," the official at the U.S. embassy in Tripoli told Reuters. Amin Salam, of the National U.S.-Arab Chamber of Commerce, said some delegates of the U.S. trade mission had arrived in Tripoli on Wednesday. "They may still go to Benghazi," he said. Some observers have raised the prospect of an insurgency breaking out in Libya along the lines of the violence that followed the U.S.-led invasion of Iraq in 2003. Security experts though say this is unlikely, not least because, unlike in Iraq, the United States has no military presence in Libya. Experts on militant groups had been predicting that the killing of Libi, described by U.S. officials as a major blow to al Qaeda, would provoke some kind of backlash inside his home country. Though he spent much of his life outside Libya, he was a member of the now-defunct Libyan Islamic Fighting Group, which fought an insurgency against Gaddafi in the 1990s, and he has several relatives still in Libya. Police in Benghazi on Wednesday had cordoned off the central Venezia street, where the U.S. mission is located, preventing a Reuters reporter from viewing any damage from the blast. Benghazi is a coastal city 1,000 km east of Tripoli where the uprising against Gaddafi began last year and where many international organisations have representative offices. It has become one of Libya's more dangerous locations. On May 22, a rocket-propelled grenade hit the offices of the International Committee of the Red Cross in the city, blasting a small hole in the building but causing no casualties. Underscoring the lack of proper security in Libya, a disgruntled volunteer militia this week occupied Tripoli international airport for several hours, leaving bullet holes in at least one jet and forcing airlines to cancel flights. Additional reporting by Hadeel Al Shalchi, Ali Shuaib and Marie-Louise Gumuchian in Tripoli and William Maclean in London; Editing by Rosalind Russell