"Dismissed" or "resigned under pressure"?

From the AP:

Energy Secretary Samuel Bodman on Thursday dismissed the chief of the country’s nuclear weapons program because of security breakdowns at the Los Alamos, N.M., laboratory and other facilities. Linton Brooks said he would leave in two weeks to three weeks as head of the National Nuclear Security Administration, a post he held since May 2003.

From Reuters:

The head of the U.S. nuclear weapons program resigned under pressure on Thursday following repeated security lapses at the Los Alamos National Laboratory.