The Republican co-authors of a bipartisan immigration reform effort denounced suggestions Friday from conservatives that the terrorist attacks in Boston were evidence that the United States should abandon a sweeping overhaul of its border control laws.

Federal authorities on Friday revealed that the two brothers suspected in the bombings were ethnic Chechens who came to the country as minors with their family in the early 2000s. They had been living in the Central Asian republic of Kyrgyzstan and were prevented from resettling in war-racked Chechnya.

The family was granted U.S. visas under provisions aimed at protecting migrants from political, religious or ethnic persecution.

The revelations prompted conservative critics of immigration reform to cast doubt on a sweeping 844-page reform bill introduced by an eight-member Senate group this week. At the first Judiciary Committee hearing on the bill Friday, Sen. Charles E. Grassley (R-Iowa) questioned whether lawmakers were rushing forward too quickly.

“While we don’t yet know the immigration status of the people who have terrorized the communities in Massachusetts, when we find out, it will help shed light on the weaknesses of our system,” Grassley said Friday morning as details of the case were still emerging. “How do we ensure that people who wish to do us harm are not eligible for benefits under the immigration laws, including this new bill before us?”

Conservative bloggers and radio hosts made similar arguments after authorities identified the bombing suspects as Tamerlan Tsarnaev, 26, and his 19-year-old brother, Dzhokhar. The older brother was reportedly killed during a shootout with authorities; the younger one — who recently became a naturalized U.S. citizen — was the focus of a massive manhunt Friday.

Bryan J. Fisher, a conservative radio host, wrote on Twitter that the Senate’s “amnesty plan” is dead on arrival. Rep. Steve King (R-Iowa), a leading immigration critic, said that the Boston bombing “brings a spotlight on this. We do want to look at these individuals and see if they happen to be a cell, how they were radicalized, if they traveled overseas.”

Several Republican members of the Senate immigration group quickly sought to rebut the conservatives.

“Some have already suggested that the circumstances of this terrible tragedy are justification for delaying or stopping entirely the effort,” Sens. John McCain (Ariz.) and Lindsey Graham (S.C.) said in a joint statement. “In fact, the opposite is true: Immigration reform will strengthen our nation’s security by helping us identify exactly who has entered our country and who has left.”

Alex Conant, a spokesman for Sen. Marco Rubio (R-Fla.), said that Americans “will reject any attempt to tie the losers responsible” for the attacks with law-abiding immigrants.

The Senate bill would eliminate a provision that requires people to file for asylum protection within one year of arriving in the United States. Advocates argue that the provision is unneccessarily restrictive because many asylum-seekers are not in position to file paperwork in English so soon after entering the country, often after fleeing a dangerous situation.

Immigrants can apply for asylum after entering the United States or they can apply for refu­gee status while still living in their home countries. Nearly 25,000 people were granted asylum and 56,400 were admitted as refugees in 2011, according to the Department of Homeland Security.

Those who qualify must undergo a criminal background check. Once admitted, they are allowed to earn a green card after five years, or three years if they are married to a U.S. citizen.

In the asylum category, about 8,600 came from China, followed by about 1,100 from Venezuela and 1,000 each from Ethi­o­pia and Egypt. Russia ranked seventh with 663. Advocates said it is rare for asylum seekers to come from Chechnya.

Discuss this topic and other political issues in the politics discussion forums.