Washington  - US President George W Bush telephoned his new Pakistani counterpart, Asif Ali Zardari, Tuesday to offer his "full support" in the fighting against Islamic militants in the country.

"Defeating these terrorists and extremists is in Pakistan's interest," Bush said in a speech at National Defence University in Washington. "They pose a mortal threat to Pakistan's future as a free and democratic nation."

Zardari took office on Tuesday and succeeds Pervez Musharraf, one of the most important US allies in the war on terrorism, who also shared a close personal relationship with Bush.

Musharraf, facing impeachment in parliament, resigned in August.

The United States has been frustrated by Pakistan's response to Taliban and al-Qaeda militants who used a remote region of the country as a refuge for launching attacks against US-led coalition forces in Afghanistan.

Pakistan is also facing a rising tide of Islamic extremism that Western analysts have increasingly identified as a major international threat.

"Defeating these terrorists and extremists is also Pakistan's responsibility because every nation has an obligation to govern its own territory and make certain that it does not become a safe haven for terror," Bush said.

Zardari, after taking the oath of office, pledged in Islamabad to face the challenge posed by extremism "head on" and expressed confidence that his country could defeat the militants.

White House spokeswoman Dana Perino said Bush looked forward to meeting with Zardari during ceremonies September 23 to 25 marking the beginning of the UN General Assembly in New York. (dpa)