WASHINGTON (AP) _ A 22-year-old California research assistant died in a diving accident Saturday under the ice of Antarctica, the National Science Foundation announced.

Mark T. Macmillan of San Jose was pronounced dead by Navy doctors at McMurdo Station, the main U.S. scientific outpost on the continent, said foundation spokewoman Karen Lebovich.

She did not have details of the accident but said diving operations at McMurdo Station had been suspended, pending an investigation.

The foundation said in a statement that a helicopter was summoned to the research site at New Harbor by radio calls from other members of a research team headed by William L. Stockton of the Marine Biology Research Division of Scripps Institution of Oceanography, which is part of the University of California at San Diego.

Macmillan was then flown the 50 miles to McMurdo Station, where he was pronounced dead, the foundation said.

The group was diving under the ice cover of McMurdo Sound to learn more about the role of predatory foraminifera, single-celled animals that live beneath the ice. The foundation said the project is part of the U.S. antarctic program which it funds.

Lebovich said Macmillan, a graduate of the University of California at Santa Cruz, was a certfied diver with experience off the northern California coast.