DUBAI (AFP) - Yemen's opposition on Sunday urged Gulf leaders to ensure a swift leadership transition to prevent a power vacuum in the deeply tribal country amid uncertainty over President Ali Abdullah Saleh's health. "Our Gulf brothers should quickly adopt firm positions to immediately and peacefully transfer power to the vice president," Abdrabuh Mansur Hadi, parliamentary opposition spokesman Mohammed Qahtan told AFP. Saleh was flown to Riyadh on June 4 for treatment a day after he was wounded when an explosion ripped through a mosque where he was praying inside his Sanaa presidential compound. He is reported to be in poor condition and suffering breathing problems in a Saudi hospital, an informed source said on Saturday. "Time is not in favour of Yemen's stability," Qahtan warned on Sunday. He urged the Gulf monarchies to push forward "an immediate transfer of power... to enable us to support the vice president and implement the rest of the Gulf initiative to resolve Yemen's crisis and restore peace and stability." Gulf Arab foreign ministers, who suspended their mediation efforts on Yemen on May 23, are set to meet on Tuesday. Saleh has steadfastly refused to sign a Gulf-brokered initiative that would see him transfer power to his deputy Hadi within 30 days in return for immunity from prosecution. Speedy Gulf intervention is needed so "Yemenis don't find themselves forced to rally behind the revolution youths" calling for the formation of an interim ruling council. Hadi has so far not responded to mounting pressure to set up the proposed council, as ruling party officials insist that Saleh is still president. At least 200 protesters have been killed in Yemen in more than four months of protests demanding the ouster of Saleh, who has been in office since 1978. Admiral Michael Mullen, the highest-ranking officer in the US armed forces, said on Wednesday that the conflict in the Arabian Peninsula country was making the Al-Qaeda terror network more "dangerous." Clashes on Sunday in the flashpoint southern city of Zinjibar killed a Yemeni colonel, two soldiers and four suspected Al-Qaeda militants, a military official and medics said. Meanwhile, five people have been arrested over suspected links to the bomb attack that wounded Yemeni President Ali Abdullah Saleh on June 3, a diplomat in Yemen told AFP on Sunday. Some 50 people have so far been questioned, the source said by telephone, requesting anonymity and declining to provide further details. Saleh was flown to Saudi Arabia for treatment of wounds sustained in the attack on a mosque in his Sanaa presidential compound. He has not been seen in public since the attack, amid conflicting reports on his condition. In an audio statement broadcast on state television on the day of the attack, Saleh appeared to blame the explosion on dissident tribal chief Sheikh Sadiq al-Ahmar, whose fighters clashed with government forces after a power transfer deal collapsed last month. The powerful tribal chieftain denied any involvement in the attack. Saleh's government then blamed the attack on Al-Qaeda, and others said it could even have been a drone strike because of its accuracy. US experts on Thursday said the attack was an assassination bid, probably an "inside job" using an improvised explosive device. STRATFOR, a US-based authority on strategic and tactical intelligence issues, said its assessment was based on an evaluation of photographs taken of the blast site. Other top Yemeni officials, including caretaker Prime Minister Ali Mohammad Mujawar and parliament chief Abdulaziz Abdulghani, were wounded in the blast that killed 11 people and injured another 124.