Street clashes between security forces and supporters of challenger Mousavi picked up after dark on Sunday after President Ahmadinejad addressed thousands of his supporters in Tehran.
He has made an effort to reach out to Iran. But charges of vote fraud and a crackdown on protesters there this weekend make it harder for the president to maintain that course.
President Ahmadinejad's bellicose rhetoric has raised concerns about Iran's intentions. Whether or not he is reelected Friday, here's what Western policymakers now need to consider.
His challenger, Mir Hossein Mousavi, is claiming irregularities. Police moved quickly to quell small protests.
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.