The United States praised Pakistani president Pervez Musharraf as a committed partner against terrorism and pledged after his resignation today to keep helping Pakistan fight extremism.
The White House said president George W. Bush was committed to a strong Pakistan that strengthens democracy and fights terrorism.
"President Bush appreciates President Musharraf's efforts in the democratic transition of Pakistan as well as his commitment to fighting al-Qaeda and extremist groups," White House spokesman Gordon Johndroe said in Texas, where Mr Bush is at his ranch.
Mr Musharraf resigned to avoid impeachment charges nearly nine years after taking office in a coup. He was an important ally for Washington in the US-declared "war on terror" and Pakistan received billions of dollars in US counterterrorism aid during his government.
But US officials have recently voiced frustration with Pakistan's efforts as the Taliban and al-Qaeda regrouped in its remote tribal areas, where some American officials and analysts say al-Qaeda leader Osama bin Laden is hiding.
Secretary of state Condoleezza Rice praised Mr Musharraf today for having made the "critical choice" to join the battle against al-Qaeda, the Taliban and other extremists.
"For this, he has our deep gratitude," she said.
"We will continue to work with the Pakistani government and political leaders and urge them to redouble their focus on Pakistan's future and its most urgent needs, including stemming the growth of extremism, addressing food and energy shortages, and improving economic stability," Ms Rice said in a statement.
"The United States will help with these efforts to see Pakistan reach its goal of becoming a stable, prosperous, democratic, modern, Muslim nation," she added.
Speculation Mr Musharraf would resign had mounted since Pakistan's fractious coalition government, led by the party of assassinated former prime minister Benazir Bhutto, said this month it planned to impeach him.
The United States, apparently resigned to Mr Musharraf's exit, had said Pakistan's leadership was a Pakistani issue.
Some concerns of Pakistan's coalition government complement US priorities, said Teresita Schaffer, director of the South Asia Program at the Centre for Strategic and International Studies.
She said both former prime minister Nawaz Sharif and Asif Ali Zardari, Ms Bhutto's widower, wanted to get Pakistan's domestic insurgency under control. "That is their top priority," Ms Schaffer said.
"For the US, arguably the top priority is border control between Pakistan and Afghanistan. But these two go together," she said.
Ms Schaffer also said the coalition government had the support of the army, "or probably Musharraf wouldn't have resigned."