Since the September 11, 2001 attacks - which led the US to invade Afghanistan and make Pakistan its regional strategic ally - Pakistan has spent about $35bn to confront fighter groups, Zardari wrote.
"Pakistan alone cannot bear the huge social and economic burden of this war. Clearly we need massive international assistance," Zardari said.
He said Pakistan would present a nine-point plan to donors at the Tokyo conference that covers fiscal stability, poverty alleviation, agriculture, industry and trade, training, energy, public-private partnerships, money markets and administrative reforms.
Economists say up to 40 per cent of Pakistan's 160 million people live on one dollar a day or less.
Zardari's comment was published a day after a suicide bomber blew up a vehicle packed with explosives at a police checkpoint in northwest Pakistan, killing 18 police and civilians.
The incident happened late on Wednesday in Charsadda, north of Peshawar, the main city of the North West Frontier Province.
|A suicide blast in Charsadda killed 18 police and civilians on Wednesday [AFP]
Pakistan security troops are frequent targets for attacks by groups who oppose the government's policies, in particular, its security ties with the US.
"Police were searching a vehicle when a mini-truck came and blew up," a senior police official said.
"Bodies of two civilians were found near the site of the attack, raising the death toll in the attack to 18," a local police chief said.
Police said they retrieved video footage from a damaged vehicle at the scene, showing two boys wearing suicide jackets, who looked like teenagers. One recited from the Quran and the second was shown smiling, the police chief said.
"We cannot say at this stage whether the two boys were the attackers or someone else did it," he said.
There has been no claim for the attack, which left a large crater, shattered windows in nearby buildings and severed power cables, plunging the area into
'Scrap Swat pact'
Against this backdrop of continuing violence, an international human rights group has urged Pakistan to reverse its decision to enforce sharia in Swat in the northwest, saying the deal threatens women and takes the region back to the Dark Ages.
Human Rights Watch said the government's move amounted to granting the Pakistani Taliban "de-facto administrative control of the Swat valley" and "presents a grave threat to the rights of women and other basic rights in the troubled region".
There still remain many questions about the exact nature of the pact, including who will have final authority over the appointment of judges trained in Islamic law.
Defenders say the deal will drain public support for extremists who have hijacked long-standing calls in Swat for reform of Pakistan's ineffective justice system.
But critics worry it rewards extremists who have beheaded political opponents and burned scores of schools for girls in the name of Islam.