Pakistan's fourth nuclear reactor now operational?

Pakistan's fourth heavy water reactor at Khushab nuclear site which allows it to build a larger number of miniaturised plutonium-based nuclear weapons now appears to be operational, a US think-tank has said.

The reactor is part of Pakistan's programme to increase the production of weapons-grade plutonium.

"A recently purchased Digital Globe high resolution satellite image dated January 15, 2015 shows that Khushab's fourth reactor's external construction is complete and has become operational," David Albright and Serena Kelleher-Vergantini of the Institute for Science and International Security (ISIS) said on Friday.

"This assessment is based on the presence of a very specific signature: steam is venting from the reactor's cooling system," he said.

Pakistan's nuclear arsenal is increasing at a pace faster than any other country and now is reported to have more nuclear weapons than that of India.

Albright and his co-author said Pakistan's Khushab nuclear site, located 200 kilometres south of Islamabad, is dedicated to the production of plutonium for nuclear weapons.