Alarmed by a slew of terror attacks on sensitive military installations in Pakistan, the US is putting in place "a crack unit" of its elite troops to seal off that country's nuclear weapons and ensure they do not fall into the hands of militants, a media report in London claimed today. It said the specialised unit would be charged with recovering the nuclear materials and securing them.<br/><br/>Pakistan is thought to possess about 80 nuclear warheads.Although the United States has provided USD 100 million worth of technical assistance to Islamabad under its nuclear protection programme, US personnel have been denied access to most Pakistani nuclear sites, the media report said.