Published: Feb 10, 2011 7:21 PM EST
Updated: Feb 10, 2011 4:21 PM EST

WASHINGTON (AP) - An independent expert says Pakistan has begun building what appears to be a fourth plutonium reactor, increasing concerns that the volatile nation is creating more nuclear material than it can safeguard.

David Albright of the Institute for Science and International Security said Thursday commercial satellite images show that construction has begun of a building near three other plutonium reactors at Khushab, outside Islamabad. He said based on its footprint it is probably a fourth reactor.

He said Pakistan may already have 100 nuclear warheads, and is currently building about 10 more each year.

The U.S. and Pakistan have long insisted that Pakistan's stockpile of weapons and nuclear material is secure. But outside experts caution that as the arsenal grows, so does the risk of theft or diversion.

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