Mr Zardari said many people had underestimated the Taleban
Pakistan's president says his country is fighting for its survival against the Taleban, whose influence he said has spread deep into the country.
In an interview with US TV channel CBS, President Asif Zardari said the Taleban had established a presence across "huge parts" of Pakistan.
The country had failed to increase its forces in response, he said.
On Saturday, officials said at least 27 militants were killed in a suspected US missile strike on a Taleban hide-out.
The missile hit a house in north-west Pakistan, near the border with Afghanistan, where the US has carried out more than 20 air strikes from drones in recent months.
Islamabad has long argued that the strikes complicate its fight against insurgents, and violate its sovereignty.
Pakistani leaders had said they hoped US President Barack Obama's new administration would halt them.
But earlier this week Mr Obama said there was no doubt militants were operating in safe havens in Pakistan's tribal belt and that the US would make sure Pakistan was a strong ally in fighting that threat.
In his interview with CBS, which is due to be broadcast on Sunday, Mr Zardari rejected any notion that Pakistan was battling the Taleban on behalf of the US.
"We're not doing anybody a favour," he said.
"We are aware of the fact [the Taleban are] trying to take over the state of Pakistan," he said.
"So, we're fighting for the survival of Pakistan. We're not fighting for the survival of anybody else."
He also said the Taleban had extended its presence from the tribal areas to Pakistan's larger cities.
"[The Taleban] do have a presence in huge amounts of land in our side," he said, according to excerpts of the the interview.
"It's been happening over time and it's happened out of denial. Everybody was in denial."
He said that many people had thought of the Taleban: "They're weak and they won't be able to take over… they won't be able to give us a challenge.
"And our forces weren't increased… we have weaknesses and they are taking advantage of that weakness."
'Way of life'
Mr Zardari was elected months after his wife, former Pakistani Prime Minister Benazir Bhutto, was assassinated at an election campaign.
Pakistan cannot allow a repeat of the December 2007 attack, he said.
"I lost my wife to it. My children's mother.
"It's important to stop them and make sure that it doesn't happen again and they don't take over our way of life," he said.
"That's what they want to do."
Witnesses of Saturday morning's missile strike in South Waziristan said it targeted a house frequented by militants from Pakistani Taleban leader Baitullah Mehsud's organisation.
Mehsud is believed to be responsible for a number of atrocities, including Ms Bhutto's assassination.
The missile strike took place during a visit to the region by US President Barack Obama's special envoy for Afghanistan and Pakistan, Richard Holbrooke, who is assessing strategic options for the future.