US President George W Bush says he is confident China stands "side by side with the American people" during the military strikes on Afghanistan.
But Chinese President Jiang Zemin cautioned the United States to "avoid innocent casualties."
Mr. Bush claims he is satisfied with China's cooperation on intelligence gathering and pursuing financial assets of al-Qaida.
"There was no hesitation, there was no doubt they'd stand with our people during this terrible time," he said at a joint news conference.
Jiang Zemin says he was "pleased to note that recently, there's been an improvement in our ties."
The two leaders are meeting on the eve of the Asia-Pacific Economic Cooperation summit.
President Bush spoke of the anthrax cases in the United States. He says there was no direct link to foreign interests such as al-Qaida or Iraq, but pledged: "Our nation will do what it takes to bring them to justice."
He does not rule out the possibility the anthrax attacks are acts of domestic terrorism, and vowed to prosecute those who carry out anthrax hoaxes.
Bush is also refusing to confirm reports US special forces are in north and south Afghanistan for ground combat. "I will not comment on ... military operations," he said.
Jiang gave qualified support of the military action in Afghanistan, saying there must be "clearly defined targets" and the United States must "avoid innocent casualties."