U.S. Sen. John Cornyn, R-Texas, expressed concern about the Obama administration's reluctance to characterize the violent events at Fort Hood as an act of terrorism.

Cornyn joins a growing number of Republicans asking for more action on the Nov. 5 shooting rampage in which 13 were killed and more than 30 injured.

In a letter sent to Obama on Tuesday, Cornyn said it appeared "increasingly probable that the Fort Hood attacker may have been motivated by a fanatical religious ideology, and this should serve as a wake-up call for federal officials."