The fallout from the fatal bombings in Boston that federal officials said was staged by two Chechen nationals, is rippling through the debate over immigration reform now underway in the Senate despite reform supporters's insistence that the issues are unrelated.

Sen. Rand Paul, R-Ky., wrote Monday to Senate Majority Leader Harry Reid, D-Nev., requesting that no reforms advance until "a thorough examination" of the Boston bombing is complete. Paul also wants to add a national security provision to the bill that would "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."

The House and Senate are crafting their own immigration reform proposals. The Senate version, released last week by a bipartisan group of lawmakers known as the Gang of Eight, would provide a pathway to citizenship for the nation's 11 million illegal immigrants, increase the number of work visas and add to border security.

The two brothers accused in the Boston Marathon bombings came to the United States legally and the younger brother became a naturalized citizen on Sept. 11, 2012.

"Why did the current system allow two individuals to immigrate to the United States from the Chechen Republic in Russia, an area known as a hotbed of Islamic extremism, who then committed acts of terrorism?" Paul wrote to Reid. "Were there any safeguards? Could this have been prevented? Does the immigration reform before us address this?

Even as Paul was calling for a delay, the Senate Judiciary Committee on Monday took up the current Senate proposal at a hearing in which Democratic supporters of the plan chided those trying to use the Boston attack to derail immigration reform.

"Last week opponents of comprehensive immigration reform began to exploit the Boston Marathon bombing," Judiciary Committee Patrick Leahy, D-Vt., said. "Let no one be so cruel as to try to use the heinous acts of these two young men last week to derail the dreams and futures of millions of hard-working people."

The committee's top Republican, Sen. Charles Grassley, of Iowa, said neither he nor other critics are exploiting the bombing, but simply want to ensure "every base is covered" during the immigration debate.

"And I want you to take note of the fact that when you propose gun legislation, I didn't accuse you of using the [Sandy Hook Elementary School] killings as an excuse," Grassley told Leahy.

Sen. Marco Rubio, R-Fla., a principal author of the Senate plan, joined with those linking immigration reform to the Boston bombings. Rubio said in a statement that if the bombings expose weaknesses in the current immigration system, "any immigration reform passed by Congress this year should address those flaws."

Rubio recommended revisiting the National Security Registration System, which provided stricter screening for immigrants coming from countries known to harbor extremists before being suspended in 2011.

White House spokesman Jay Carney said that immigration reform itself would improve national security.

"The process of moving along the earned path to citizenship and the various hurdles that have to be cleared in that process allows for much more information to be known by the relevant authorities and agencies about these individuals," Carney said.