The U.S. refugee program has come under fresh criticism after federal authorities revealed that two Iraqi-born men arrested on terrorism-related charges had come to America as refugees. While there was no evidence the men intended or planned attacks in the United States, Republican lawmakers already concerned about the federal government's ability to properly vet Syrian refugees said the cases highlight weaknesses in the program that put Americans' safety at risk. "How many ticking time bombs are we going to bring in in this refugee program without a proper vetting system in place?" Rep. Michael McCaul, chairman of the House Homeland Security Committee, said at a news conference Friday. He and other Republican lawmakers urged the Senate to pass legislation to block refugees from Iraq and Syria until screening is improved. The House passed a bill in November. The uproar comes after weeks of fervent debate in Washington and on the presidential campaign trail about tighter security screens in the wake of attacks in Paris and San Bernardino, California. Immigrant advocates said they have full confidence in the vetting process and that tens of thousands of Iraqi refugees have been successfully resettled under the program. On Thursday, federal authorities in California accused 23-year-old Aws Mohammed Younis Al-Jayab, of Sacramento, of traveling to Syria to fight and lying to U.S. officials about it. Al-Jayab had come to the United States as a refugee in October 2012, and discussed on social media how he fought against the regime in Syria as a teen, authorities said. In Texas, 24-year-old Omar Faraj Saeed Al Hardan, of Houston, was indicted on charges that he tried to provide material support to the extremists. Both suspects are Palestinians born in Iraq, authorities said. The U.S. annually accepts 70,000 refugees from around the world, including people fleeing violence, religious persecution and war, and has announced plans to increase the number to 85,000 this year.