US still committed to defeating al-Qaeda: Obama

President Barack Obama warned on Wednesday of more violence in Pakistan and Afghanistan, but said his government was still committed to defeating al-Qaeda, while trying to avoid civilian deaths on those countries.

Obama brought the Afghan and Pakistani presidents to the White House and said both leaders reaffirmed their commitment to the battle against al-Qaeda.

The Obama administration had sharply criticized both Hamid Karzai and Asif Ali Zardari in the past, questioning their commitment and capability to tackle the threat from al-Qaeda and the Taliban.

On his part Zardari is seeking U.S. military aid and political support, while Karzai hopes to purge Taliban havens in Pakistan, which are destabilizing his country.

"The road ahead will be difficult. There will be more violence and there will be setbacks," Obama said, with Afghanistan's Karzai and Pakistan's Zardari at his side.

"But let me be clear -- the United States has made a lasting commitment to defeat al-Qaeda but also to support the democratically elected sovereign governments of both Pakistan and Afghanistan. That commitment will not waiver and that support will be sustained."

The road ahead will be difficult. There will be more violence and there will be setbacks

U.S. President Barack Obama

Civilian casualties in Afghanistan

The talks coincided with fresh reports from Afghan police and the Red Cross that U.S.-led air strikes targeting insurgents had killed 100 people, most of them civilians, in one of the deadliest battles since the fall of Taliban in 2001.

U.S. Secretary of State Hillary Clinton offered her deep regret for the incident, without implying U.S. responsibility for it. An American official who asked not to be named said it appeared that U.S. bombing may have caused the deaths.

Civilian casualties caused by U.S. military operations in both countries, including drone strikes inside Pakistan, are deeply unpopular among Afghans and Pakistanis and have made it harder for both countries' leaders to cooperate with the United States.

"We deeply, deeply regret that loss," Clinton said of the civilian deaths as she began a meeting with Karzai and Zardari. Later she called that meeting "in some ways a breakthrough" and said she was "very optimistic" the process was making a difference.

We deeply, deeply regret that loss

U.S. Secretary of State Hillary Clinton

Obama announced a new approach to the fight against al-Qaeda in both countries in late March, offering more aid but also more than 20,000 extra troops to Afghanistan this year.

"We turned a corner," Richard Holbrooke, the U.S. special representative for Afghanistan and Pakistan, told reporters after Obama's brief address. "We gave physical reality to the strategic plan."

Karzai, whose office said earlier that he called the civilian deaths "unjustifiable and unacceptable," thanked Clinton for expressing concern and regret, saying he hoped all civilian casualties could be prevented.

Pakistan's democracy needs support

Zardari, who has been under fierce criticism for his response to Taliban militants who have made inroads in the Swat and Buner valleys this year, pleaded for support for his fledgling democracy.

"My democracy needs attention and needs nurturing," Zardari said. "Pakistani democracy will deliver and the terrorists will be defeated by our joint struggle. Me, my friend President Karzai and the United States ... will stand shoulder to shoulder with the world to fight this cancer and this threat."

Many Pakistanis blame America for undermining democracy in their country for decades by supporting and funding its powerful military, but Clinton said U.S. support for the democratic government was "very, very firm."

She also asked for U.S. understanding and patience for Zardari, just eight months into his new job.

"He inherited a very difficult and unmanageable situation," she said. "I think a little more understanding on our part about what he confronted -- you know, he has successfully navigated some real crises."

The Washington talks came amid fresh waves of deadly clashes in Pakistan's Swat valley in which the military said it had killed more than 80 militants in an upsurge of fighting on Wednesday.

Pakistan's cash-strapped government was making emergency preparations to shelter up to 500,000 people expected to flee Swat and local officials said tens of thousands had already left the district's main town.

Me, my friend President Karzai and the United States ... will stand shoulder to shoulder with the world to fight this cancer and this threat

Pakistani President Asif Ali Zardari