ISLAMABAD: Pakistani authorities sacked some people having "negative tendencies" working with the country's sensitive nuclear programme to keep it safe, according to a report.

"We filtered out people having negative tendencies that could have affected national security," said Brig (retd.) Tahir Raza Naqvi, who works for strategic plans division, the administering body for the nuclear programme.

Those sacked were the "incorrigible" ones, he said, and quickly added: "Our checks are very solid."

The sacked nuclear workers could not clear the personnel reliability programme that was started in mid-2003/04 to screen the employees working on the sensitive programme, Naqvi was quoted as saying by the Dawn.

He was addressing a seminar on Wednesday on 'Future security outlook of South Asia: Trends and challenges' organised by an Islamabad-based thinktank, Centre for International Strategic Studies, and Konrad Adenauer Stiftung of Germany.

Naqvi said all employees of the nuclear programme are periodically checked for family background, education, political affiliation and religious inclinations.

He would not say how many were sacked over the years or why they failed to clear the screening.

At least 12 people linked to disgraced nuclear scientist Dr Abdul Qadeer Khan were removed when the proliferation scandal surfaced in 2003. But those firings took place before personnel reliability programme was instituted.

Prof Siegfried Hecker of Stanford University said Pakistan had real security concerns and its perceived need for a robust strategic deterrent was now recognised by the West.

However, he said that concerns remained about the increase in fissile material production and development of diverse delivery systems (missiles).

He said Pakistan must keep its nuclear weapons, material and know-how under strict government control.

"Safety and security is paramount to manage nuclear enterprise," he maintained, adding that safety and security was "not a destination, but a journey and the first line against nuclear terrorism".

Pakistan is believed to be sitting on something like 120 nuclear warheads and has recently brought into play two new heavy water plants that will enable them to produce about 24 nuclear warheads a year.

The West fears Pakistan's nuclear arsenal could be vulnerable to penetration by militant groups.