ISTANBUL — The United States and dozens of other countries moved closer on Sunday to direct intervention in the fighting in Syria, with Arab nations pledging $100 million to pay opposition fighters and the Obama administration agreeing to send communications equipment to help rebels organize and evade Syria’s military, according to participants gathered here.

The moves reflected a growing consensus, at least among the officials who met here this weekend under the rubric “Friends of Syria,” that mediation efforts by the United Nations peace envoy, Kofi Annan, were failing to halt the violence that is heading into its second year in Syria and that more forceful action was needed.

With Russia and China blocking United Nations measures that could open the way for military action, the countries lined up against the government of President Bashar al-Assad sought to bolster Syria’s beleaguered opposition through means that seemed to stretch the definition of humanitarian assistance and blur the line between so-called lethal and nonlethal support.

There remains no agreement on arming the rebels, as countries like Saudi Arabia and some members of Congress have called for, largely because of the uncertainty regarding who exactly would receive the arms.