"This is an existential battle. If we lose, so too will the world. Failure is not an option," Zardari said, a day after Pakistan was rocked by a brazen terror attack on Sri Lankan cricketers, the first in the history of cricket.

"Tuesday's terrorist attack against the Sri Lankan cricket team in Lahore [Images] shows once again the evil we are confronting," the Pakistan President said in an op-ed piece in the Wall Street Journal.

Touching on the issue of growing militancy in his nation, Zardari said, "We have not and will not negotiate with extremist Taliban [Images] and other terrorists".

Defending the recent truce reached in the "highly volatile" Swat, Zardari said, "The clerics with whom we have engaged are not Taliban, and it is their responsibility to rein in and neutralise Taliban and other insurgents".

Zardari warned that if the truce did not work out and the Taliban militants did not lay down their arms, the security forces will act accordingly.

"In Swat, our strategy has been to enter into talks with traditional local clerics to help restore peace to the area, and return the writ of the state," he wrote.

Zardari also said that his government will not condone the closure of girls' schools in the Swat valley, insisting that education of women was "mandatory".

Reflecting on the recent trilateral meeting between the United States leaders, ministers and top officials from Afghanistan and Pakistan, he said this was a crucial step forward in the war on terror and fanaticism in South and Central Asia.

The Pakistan president disclosed that this was for the first time that Washington, Kabul and Islamabad [Images] had agreed on a coherent military and political strategy to isolate the terrorists.

Zardari said, "Islamabad had made it known to Washington that if we are to prevail on the ongoing battle against terrorism then straight talk is essential."

"And this straight talk begins with a fact: Pakistan's fight against terrorism is relentless," he said.

"But the process of weaning reconcilable elements of insurgency away from hardliners had been mischaracterised in the West," Zardari added.