US Secretary of State Hillary Clinton on Wednesday asked Pakistan to face up to the gravity of threat posed by nuclear weaponised terrorists group in its midst as it urged the country to join nuclear non-proliferation process.Clinton who arrived in Islamabad on a three-day visit told reporters that, al-Qaida and their extremist allies are always on the hunt for nuclear material and it doesn't take a lot to create a very damaging explosion with extraordinary political ramifications. While asserting that Washington has a high degree of confidence that Pakistan's nuclear weapons were safe, Clinton said that Washington is worried about proliferation. On her arrival, she said that several civilian investment deals would be signed during her visit.