Now we know why Ann Curry was filling in on Nightly News last night: Brian Williams was on his way to Afghanistan.

Williams will anchor and report from the region for the next several days, but for security reasons, the details of the travel schedule are being kept secret. NBC does say he and correspondent Martin Fletcher will "be spending time with U.S. forces engaged in the fight against the Taliban."

Williams is a veteran of four trips to Iraq during the current war.

Williams interviewing Paul Fishstein, Director of AREU, for a story that will air on tonight's Nightly News. (Photo: Subrata De/NBC)