US Army Major Nidal Hasan, accused of killing 13 people at Fort Hood, Texas, intensified contacts with a radical Yemeni American cleric just months before the shootings and began discussing surreptitious financial transfers, The Washington Post reported Saturday.

Citing two unnamed sources briefed on a collection of secret e-mails between the two, the newspaper said the e-mails were obtained by an FBI-led task force in San Diego between late last year and June but were not forwarded to the military.

Some were sent to the Federal Bureau of Investigation's Washington field office, triggering an assessment into whether they raised national security concerns, but those intercepted later were not, the report said.

Hasan's contacts with extremist imam Anwar al-Aulaqi began as religious queries but took on a more specific and concrete tone before he moved to Texas, the paper noted.

One source said the two discussed in "cryptic and coded exchanges" the transfer of money overseas in ways that would not attract law enforcement attention, according to The Post.

"He (Hasan) clearly became more radicalized toward the end, and was having discussions related to the transfer of money and finances," the paper quotes on of the sources as saying. "It became very clear toward the end of those e-mails he was interested in taking action."

Senate Armed Services Committee Chairman Carl Levin said Friday that he would investigate the handling of the e-mails and why military officials were not aware of them before the deadly attack.

According to The Post, Levin told reporters after a briefing from Pentagon staff members that "there are some who are reluctant to call it terrorism, but there is significant evidence that it is."