WASHINGTON – Senator Rand Paul on Monday called for Congress to focus on strengthening national security before considering comprehensive immigration reform, in the wake of the Boston Marathon bombings allegedly masterminded by a pair of immigrant brothers from Kyrgyzstan.

“The facts emerging in the Boston Marathon bombing have exposed a weakness in our current system. If we don’t use this debate as an opportunity to fix flaws in our current system, flaws made even more evident last week, then we will not be doing our jobs,” wrote Paul, a Kentucky Republican, in a letter to Senate Majority Leader Harry Reid.

Russian authorities in 2011 had flagged Tamerlan Tsarnaev, one of the suspected bombers who died Friday following a shootout with police, as a follower of “radical Islam” and warned the FBI, which said it investigated the man but did not find evidence of terrorist activity. Tamerlan, 26, had a green card, but questions about his “moral character” were raised in the review of his application for citizenship. His younger brother, Dzhokhar Tsarnaev, 19, became a naturalized US citizen on September 11, 2012.

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The brothers are ethnic Chechens who immigrated to the United States about a decade ago as children from Kyrgyzstan, a former Soviet Republic in central Asia.

Paul is the latest in a string of conservative Republicans seeking to use last week’s Boston terrorist attacks to delay comprehensive immigration reform. The Senate Judiciary Committee continued debating the bipartisan immigration bill on Monday, its second hearing following the bill’s introduction last week. The committee is expected to continue vetting the bill through May, with the full Senate slated to begin debate on the bill in June.

Senator Patrick Leahy, a Vermont Democrat and chairman of the Senate Judiciary Committee, on Monday accused opponents of immigration reform of exploiting the Boston bombings, using it as an excuse to thwart reform.

“Last week opponents of comprehensive immigration reform began to exploit the Boston Marathon,” he said as he convened Monday’s hearings. “I urge restraint in that regard.”

Paul said no further changes should be made to immigration “until we understand the specific failures of our immigration system” and possibly an intelligence failure given that Tamerlan Tsarnaev had already been flagged by the FBI. In his letter, Paul suggested temporarily suspending student visas from high-risk countries and called for heightened scrutiny before accepting refugees from such countries.

“The Senate needs a thorough examination of the facts in Massachusetts to see if legislation is necessary to prevent a similar situation in the future,” Paul said. “National security protections must be rolled into comprehensive immigration reform to make sure the federal government does everything it can to prevent immigrants with malicious intent from using our immigration system to gain entry into the United States in order to commit future acts of terror.”

During the first senate hearing on immigration last Friday, Senator Charles Grassley, an Iowa Republican, also recommended that the Senate not rush to pass immigration reform before determining how people such as the Tsarnaev brothers “who wish to do us harm” will not stand a chance to benefit.

Senator Daniel Coats, an Indiana Republican, said on ABC’s “This Week With George Stephanopoulos” on Sunday that he agreed with Grassley to slow down the immigration debate.