Pakistan's former ambassador to Washington on Monday cast doubt on incoming prime minister Nawaz Sharif's overtures to the United States and India, saying he has a poor record on opposing extremists.

Husain Haqqani, who is close to the rival Pakistan People's Party, said that Sharif may not back up his statements with substance after the two-time prime minister's center-right Pakistan Muslim League-N triumphed in Saturday's polls.

"He will say he wants good relations with the United States and there are individual Americans with whom he has very good relations," Haqqani told a press conference call by the New York-based Council on Foreign Relations.

"Similarly, he will go ahead and engage with India. But will he really crack down on the hardline groups, many of whom campaigned for him and supported him in this election? I'm not so sure," Haqqani said.

Sharif, speaking to foreign media after his victory, promised to address any concerns of the United States and India and vowed "full support" as Washington pulls troops out of neighboring Afghanistan next year.

But Haqqani faulted Sharif for the creation of Lashkar-e-Taiba, a virulently anti-Indian Islamist movement, and noted that he was prime minister during the short Kargil war with India in divided Kashmir in 1999.

Kargil later said that the Kargil conflict was engineered by the military under its chief Pervez Musharraf, who later ousted him in a coup.

Musharraf in March returned to Pakistan in hopes of a political comeback but was instead put under house arrest on charges that include those related to the assassination of former prime minister Benazir Bhutto.

Haqqani said that Sharif was returning "with a stronger hand" in Pakistan's historic tension between the military and civilians.

"He will definitely try to assert himself far more than past civilian rulers have, including him in his previous incarnation," Haqqani said.

Haqqani said it remained unclear whether Sharif would try to punish "or at least humiliate" Musharraf in retaliation for the 1999 coup -- and what effect such action would have on relations with the military.

Haqqani, the public face of Pakistan in Washington during crises including the killing of Osama bin Laden, was forced to resign in 2011 after he was accused of seeking US help to curb the power of Pakistan's military.

He has denied wrongdoing and avoided potential prosecution by staying in the United States, where he is a professor at Boston University and a senior fellow at the Hudson Institute.