Gunman kills 13 at U.S. military base

Hasan said his cousin had been transferred to Fort Hood in April and was very reluctant to go to Iraq. "We've known over the last five years that was probably his worst nightmare," he said.

U.S. President Barack Obama called the event a "horrific outburst of violence" and promised "answers to every single question about this horrible incident."

Fort Hood is home to about 50,000 troops and stretches across 339 square miles (878 square km) in central Texas, halfway between Austin and Waco.

(Reporting by Anthony Boadle, editing by Vicki Allen)