A 25-year-old man died Sunday after being trapped beneath a large rock on Offutt Island in the Potomac River, Montgomery County fire and rescue spokesman Pete Piringer said.

Piringer described the man as a rock climber. His name was not released. It remained unclear late Sunday night how the man became trapped.

Rescuers from both Montgomery and Fairfax Counties assembled to try to extricate the man. One report indicated that authorities planned to use inflatable air bags to help move the rock. According to accounts, the man apparently died before extrication was completed. .

At one point late in the afteernoon severe storms rolled through the area, with thunder and lightning, and efforts to rescue the man were suspended, Piringer said.

The uninhabited island of trees and rocks is about three miles upstream from the American Legion Bridge. It is relatively close to the Maryland shore, but it was not clear how the man got to the island or whether he was accompanied.

Piringer said the death would be investigated by police.