Pakistan's nuclear programme was developed to make the country's defence impregnable, Prime Minister Nawaz Sharif said on Saturday, adding it was a guarantee for peace in the South Asian region.It is our national responsibility to be prepared to protect the country from internal and external threats, Sharif said in his message on the occasion of 'Youm-e-Takbeer', the day Pakistan became a nuclear power."The programme created a balance of power, which was necessary to make this region safe," Sharif said.Youm-e-Takbeer marks the day when Pakistan tested its nuclear weapons in 1998 in Balochistan province.The day comes 17 days after India carried out a series of underground nuclear tests on May 10, 1998. It was the first time India carried out such tests after 1974.He said South Asian countries came out of instability due to Pakistan's nuclear programme.