"These sanctions, though belated, are welcome," said Howard L Berman, Chairman of the powerful House Foreign Affairs Committee. But this is not enough, he argued.

Those involved in the A Q Khan nuclear black market are party to the worst proliferation of nuclear equipment and technology in history, he said.

"But the sanctions do not put an end to the matter; equipment and technology from this network may still be circulating, and new suppliers could well spring up to take Khan's place," Berman argued.

Berman said President Obama, who inherits a complex situation, must redouble US efforts against international black markets in weapons of mass destruction and ballistic missiles.

"Congress should be ready to provide new funds and the legal authorities that he may need to end the activities of these merchants of mass destruction," Berman said.

Earlier in the day, the State Department announced it has slapped sanctions on 13 individuals and three private companies for their involvement in the nuclear proliferation network of A Q Khan, the disgraced Pakistani scientist, now under house arrest.

"Dr A Q Khan led an extensive international network for the proliferation of nuclear equipment and know-how that provided "one stop shopping" for countries seeking to develop nuclear weapons," the State Department said.

The sanctions comes, the State Department says, following several years of governmental review of activities pertaining to the activities of the A Q Khan network, which is believed to have sold nuclear technologies to several countries of the world including Iran and Libya. Several countries around the world including Pakistan, South Africa, Turkey, the UAE, Britain, Germany, Switzerland and Malaysia helped the US in its investigations.

"We believe these sanctions will help prevent future proliferation-related activities by these private entities, provide a warning to other would-be proliferators, and demonstrate our ongoing commitment to using all available tools to address proliferation-related activities," said the State Department.

Khan might not be any longer active the State Department cautioned countries around the world to remain vigilant to ensure that his network, associates or others seeking to pursue similar proliferation activities, will not become a future source for sensitive nuclear information or equipment.