Sharif poised to take over as Pakistan PM

But Mr Khan added that his party was collecting evidence of alleged vote-rigging.

"PM extends his congratulations to Mr Nawaz Sharif and his party for their emphatic victory in Pakistan's elections," he said on his Twitter account.

He invited Mr Sharif to go to India "at a mutually convenient time".

Afghan President Hamid Karzai said he hoped for co-operation to root out what he called terrorist sanctuaries.

Both Pakistan and Afghanistan are engaged in a long battle with Taliban Islamist militants.

The triangular relationship between Pakistan, Afghanistan and the US will be tested more than ever as Nato withdraws combat forces from Afghanistan by the end of next year, says the BBC's Mike Wooldridge in Islamabad.

At home, Nawaz Sharif's government will be equally tested in tackling Pakistan's severe shortages of power which damage the economy and hold back job creation, says our correspondent.

In what is seen as another sign of the acute challenges facing the new government, a bomb has gone off in the south-western city of Quetta, killing at least five people.

A suicide bomber drove a car packed with explosives into the wall of the official residence of the police chief of Balochistan province, Mushtaq Shukhera.

Most of those killed are reported to be police, but one child also died.

Mr Shukhera was not among the 60 injured in the explosion, which left a large crater and was heard across Quetta. No group has claimed responsibility for the attack.

Balochistan suffers from separatist violence and sectarian conflict between Sunni and Shia Muslims.

BBC