The threat of worsening anthrax attacks raises the stakes for US President George W. Bush's mission to Shanghai for the Apec leaders' summit, according to Washington analysts.
They said the attacks had put Iraq's link to terrorism under the spotlight and increased the prospect of Washington extending military action from Afghanistan, a move likely to threaten international support.
'It could not be a more important time for the President to be meeting regional leaders,' one White House official said. 'The need to build support for what could be a long, drawn-out war against terrorism will be our priority.'
One-on-one sessions between Mr Bush and President Jiang Zemin and Russian counterpart Vladimir Putin are likely to be dominated by the issue of widening military action.
China in particular has warned military action should be limited in scope, even as it has pledged intelligence support. At the same time, senior Bush administration officials have made it clear the US does not want to see the fight against terrorism used by Russia or China to crack down on internal dissent.
US National Security Adviser Condoleezza Rice said Mr Bush would be walking a fine line in his meetings.