Chambliss' concerns were echoed by Sens. John McCain, R-Ariz., Kelly Ayotte, R-N.H., and Lindsey Graham, R-S.C., as well as Rep. Peter King, R-N.Y.
"A decision to not read Miranda rights to the suspect was sound and in our national security interests," the four said in a statement. "However, we have concerns that limiting this investigation to 48 hours and exclusively relying on the public safety exception to Miranda, could very well be a national security mistake. It could severely limit our ability to gather critical information about future attacks from this suspect."
But Rep. Adam Schiff, D-Calif., a former federal prosecutor and member of the House Intelligence Committee, said the administration should ignore "hasty calls to treat the suspect as an enemy combatant."
"This is not a foreign national caught on an enemy battlefield, but an American citizen arrested on American soil," Schiff said. "The Justice Department has demonstrated a far greater ability to successfully prosecute suspected terrorists in federal courts than the military commissions have thus far been able to show. Nothing must be done to compromise the public safety, the ability of prosecutors to seek justice for the victims or our constitutional principles."
While the Republicans asserted that Tsarnaev can be held as an enemy combatant, the Supreme Court has never resolved whether citizens or foreign nationals arrested on U.S. soil can be held by the military, as opposed to civilian authorities.
The court twice was prepared to take up that question in recent years, once while George W. Bush was president and once since Barack Obama became took office. Both times, the administration moved the suspected terrorists, U.S. citizen Jose Padilla and graduate student Ali al-Marri, from a military brig to civilian confinement to head off the high court case.
Associated Press writers Denise Lavoie in Boston and Donna Cassata and Alicia A. Caldwell in Washington contributed to this report.