An armed gang went on a rampage Saturday, gunning down four jewelry store owners and robbing more than a dozen shops in the western city of Falluja in what may have been an effort to finance insurgent groups, Iraqi authorities said. During the past month or so, violent holdups of jewelry stores selling gold products have become increasingly common in Iraq. The robberies have been attributed variously to groups like al-Qaida in Mesopotamia and on outlaw bands of soldiers and police officers. Earlier this month in the southern city of Basra, gunmen killed three people during a jewelry shop robbery. Last month, bandits killed 14 people during a string of daytime holdups of jewelry stores in Baghdad. The businesses make an inviting target: They sometimes have large amounts of cash on hand, offer a product that can be easily resold on the black market and are typically not well protected despite the value of their inventory. On Saturday, officials in Falluja blamed al-Qaida for the most recent attack, saying the militant Sunni organization was seeking to regroup after the capture of several of its leaders this year. Sheik Aifan Saadon al-Aifan, the leader of the security committee for the provincial council in Anbar Province, said Saturday that security forces in the province had been infiltrated by insurgents and their sympathizers who may have aided the robbers in Falluja. 'The insurgents are trying to gain back the power they lost,' al-Aifan said. At about 8 a.m. on Saturday, the Iraqi police said, about 20 men dressed in black and wearing black masks burst into shops in Al Bazarah market. Armed with rifles and pistols fitted with silencers, they began shooting into stores, witnesses said. After shooting dead four shop owners who may not have immediately complied with their demands, they fled with a large quantity of gold jewelry, the police said. Abu Asil, a jewelry store owner in Falluja, said Saturday that shopkeepers who had gone to the police about 10 days ago seeking increased protection were told that the police did not have enough manpower. At the funerals for the four victims on Saturday, people were angry that the robberies had occurred in a city filled with checkpoints and roving security force members. 'How can gunman so easily rob these stores?' asked Sheik Khalid Mohammed. 'Every two or three days there is an explosion. Where is the police and army? If they can't protect us, they should tell us, and we will protect ourselves.' A group with links to al-Qaida claimed responsibility for deadly raids during the past two weeks on Iraq's Central Bank and the country's Trade Bank, although robbery did not appear to have been the motive in those attacks. Also Saturday, during an oil conference in Baghdad, Iraqi officials said it would cost at least $23 billion to build four new refineries as part of the country's effort to become a net exporter of petroleum products. Iraq, which has the world's third largest amount of proven oil reserves, currently imports refined petroleum. 