The United States signed up Arab allies on Thursday to a “coordinated military campaign” against Islamic State fighters, a major step in building regional support for President Barack Obama’s plan to strike both sides of the Syrian-Iraqi frontier.

After talks in Saudi Arabia’s summer capital Jeddah, Secretary of State John Kerry won backing from 10 Arab countries – Egypt, Iraq, Jordan, Lebanon and six Gulf states including rich rivals Saudi Arabia and Qatar – for a coalition to fight the Sunni militants that have seized swathes of Iraq and Syria.

“Arab nations play a critical role in that coalition, the leading role really across all lines of effort: military support, humanitarian aid, our work to stop the flow of illegal funds,” Kerry told a news conference. […]