Even if China doesn't follow through on its vote for economic sanctions, the UN resolution approved Friday may let other countries tighten the screws.
Street demonstrations quieted ahead of intensely anticipated presidential vote on Friday.
Supporters of challenger Mir Hossein Mousavi clash with riot police and Hizbullah vigilantes.
The deal would be part of a reconciliation effort between Iraq's government and extremist Shiite groups.
US envoy Mitchell was in Egypt Thursday, and arrives in Damascus Friday. Syrians hope for a new rapprochement under an Obama administration.
His Cairo speech, combined with other early decisions, may have influenced Lebanon's election Sunday – and could have an impact on Iran's presidential vote Friday.
Tens of thousands have rallied in favor of Ahmadinejad challenger Mousavi ahead of June 12 election.