WASHINGTON—U.S. Secretary of State John Kerry is headed to Switzerland for an international conference on ending the crisis in Syria after a last-minute resolution to a spat over Iran's participation.

Kerry departed Washington before dawn Tuesday for the meeting in Montreux, which aims to set in motion the formation of a transitional Syrian government that would hold democratic elections.

Despite being a major player in the Syria conflict, Iran won't be attending because it has refused to endorse the conference's main goal.

The U.N. invited Iran on Sunday but disinvited it on Monday after the U.S., some of its allies and the Syrian opposition protested its inclusion.

Russia's foreign minister said Tuesday that the decision to disinvite Iran was a mistake but not a catastrophe.