WASHINGTON (AFP) - Satellite photos released on Tuesday show Pakistan has expanded two sites crucial to its nuclear programme as part of an effort to bolster the destructive power of its atomic arsenal, a US arms control institute claimed. The commercial images reveal a major expansion of a chemical plant complex near Dera Ghazi Kahn that produces uranium hexalfuoride and uranium metal, materials used to produce nuclear weapons, asserted analysts at the Institute for Science and International Security (ISIS). At a site near Rawalpindi, photos suggest the Pakistanis have added a second plutonium separation plant adjacent to the old one, the ISIS report said. Pakistan in recent years also has been building two new plutonium production reactors, it said. All together, these recent expansion activities indicate that Pakistan is indeed progressing in a strategic plan to improve the destructiveness and deliverability of its nuclear arsenal, the report said. The expansion would enable Pakistan to build smaller, lighter plutonium-fission weapons and thermonuclear weapons that employ plutonium as the nuclear trigger and enriched and natural enriched uranium in the secondary, it said. The satellite photos follow confirmation from the top US military officer, Admiral Mike Mullen, on Friday that Pakistan was expanding its nuclear arsenal. Mullen on Monday said US assistance to Pakistan was not being used by Islamabad to bolster its nuclear weapons programme. Given turmoil in Pakistan with the army waging war against Taliban in the northwest, the ISIS said the security of its nuclear assets remains in question. An expansion in nuclear weapons production capabilities needlessly complicates efforts to improve the security of Pakistans nuclear assets, it said. The institute urges the US government to persuade Pakistan to halt production of fissile material and join talks for a treaty that would ban the production of plutonium and highly enriched uranium. As an interim step, the United States should press both India and Pakistan to suspend any production of fissile material for nuclear weapons, it said. Pakistan has roughly 60 to 100 nuclear weapons that can be delivered by attack aircraft and ballistic missiles, the report added.