Saudi officials arrested an Al-Qaida figure suspected of masterminding the Riyadh bombings, a newspaper reported Wednesday, and the U.S. ambassador warned that militant cells are likely still plotting attacks in the kingdom. Interior Minister Prince Nayef announced new arrests, saying the hunt had intensified for those involved in the May 12 suicide bombings in the Saudi capital, which killed 34 people, including eight Americans. Saudi newspapers said that among those arrested were five people in the eastern city of Medina - including Ali Abd al-Rahman al-Faqasi al-Ghamdi, who U.S. officials say is one of al-Qaida's top figures in Saudi Arabia. Al-Ghamdi, captured along with two others at an Internet cafe, is suspected of plotting the Riyadh blasts, the daily Al-Watan reported. Al-Watan, like most Saudi papers, is privately owned but government guided. A security analyst with close ties to the government said 11 suspected militants were arrested in Medina and four others in Riyadh in the last couple of days. Among those captured in Medina were two wanted Muslim clerics - Ali al-Khudair and Ahmad al-Khalidi - arrested at a hideout where where weapons were found, the analyst said on condition of anonymity. The clerics had called for the support of the 19 wanted militants and had long been known for their sympathy for al-Qaida and the Taliban. A third wanted cleric, Nasser al-Fahd, remains at large. Nayef declined to give details in his announcement, saying only that "a number of people were arrested some days ago and (Tuesday) in Medina," the state-run Saudi Press Agency said. Saudi officials have detained about 100 people since the Riyadh car bombings, which targeted three residential compounds housing many Westerners. Still, U.S. officials worry about more attacks. "There is no indication that this was one-time ... attack," U.S. Ambassador Robert Jordan said, adding that Al-Qaida remained "a very real and persistent threat here in the kingdom." "There are very likely others out there planning parallel activities, perhaps not even in direct communication with each other, and so our concern ... goes far beyond the ability of one or two who may have escaped the attack of May 12 to carry out something else." Nine Saudi attackers were among the 34 people killed in the Riyadh bombings, but others escaped. "You have a number who have fought in Afghanistan who are hardened terrorists," Jordan told reporters at the U.S. Embassy, "you have some others who are sometimes brought into these organizations and these cells, and then you have a broader group of people who have varying degrees of sympathy for what Al-Qaida has done." Saudi Arabia says it will seek the extradition of any Saudis who may be among Al-Qaida members held in Iran and could have had a role in the bombings. Saudi Arabia extradited to neighboring Yemen four Yemeni al-Qaida suspects wanted in attacks on the USS Cole and a French oil tanker, a Yemeni security official said Wednesday. The four did not appear to have been among the 10 men accused of being key planners of the Cole bombing who escaped from a jail last month in Aden, Yemen. Al-Ghamdi, the militant reportedly captured in the latest arrests, was among 19 men wanted in connection with a weapons cache found May 6 near the site of the Riyadh bombings. The 19 were believed to be receiving orders directly from Al-Qaida chief Osama bin Laden and may have been planning to attack Saudi royal family members and U.S. and British interests. **PHOTO CAPTION*** A Saudi officer looks at the wreckage of the devastated Al-Hamra expatriate housing compound that was hit by a suicide car bombing(AFP/File/Bilal Qabalan)