ISTANBUL, Turkey — Syria’s opposition coalition voted Saturday to attend peace talks with representatives of President Bashar al-Assad’s regime in Geneva this week, setting the stage for what world leaders hope will be the first direct talks between the Syrian government and its opponents since conflict erupted nearly three years ago.
The decision was apparently eased by a surprise message of support from commanders of some of the biggest rebel groups fighting on the ground, who had been summoned by their international sponsors to a parallel meeting in Ankara, the Turkish capital.
Syrian Opposition Coalition members and rebel officials said the groups included the Islamic Front, the new alliance of Islamist factions that now forms the biggest fighting force in Syria. An Islamic Front spokesman refused to confirm or deny that it had endorsed the process, and the alliance’s top commanders are known to bitterly oppose the peace talks, leaving it unclear exactly who was behind the message.
But the arrival of the message at the secret location outside Istanbul where the coalition members were meeting helped them overcome their misgivings and take a decision on the controversial issue, said Abdulrahman Haj, one of those who participated in the vote.
‘‘It’s a very big deal,’’ he said. ‘‘It means we are going to Geneva stronger than we would have been.’’
The vote culminated months of internal wrangling that risked shattering the already fractured coalition, which is widely regarded as having failed to present a credible alternative to Syrian President Bashar al-Assad’s government since it was formed more than a year ago.
Some 45 coalition figures boycotted the vote, in a sign of the emotions stirred by the prospect of talking peace with Syria’s government, which the opposition blames for the past three years of bloodshed. Of the 75 members who took part, 58 voted yes, 14 no and 3 abstained, the coalition said, leaving the 125-member body almost evenly divided.
Coalition president Ahmad al-Jarba sought to reassure Syrians who fear that attending the talks equates to capitulation, saying the purpose was to press for Assad’s departure, not to negotiate a settlement.
‘‘We are joining the conference with our heads held high,’’ Jarba said in a statement read after the vote. ‘‘We will carry an olive branch, but we will keep hold of our guns.’’
Secretary of State John Kerry hailed the vote as ‘‘courageous’’ and pledged to continue to support the Syrian opposition as the peace talks begin. ‘‘We will stand by you every mile of the journey as you seek to achieve the freedom and dignity that all Syrians deserve,’’ he said.
The United States has spearheaded a massive campaign to persuade the opposition to attend the Geneva talks — the only solution the international community has come up with to end three years of bloodshed in Syria — and to persuade other allies of the opposition as well that the talks represent the sole hope for that outcome.
Turkey and Qatar hosted the Saturday meeting at which rebel commanders were threatened with a cut-off of aid if they did not support the peace talks, according to rebel officials who spoke to people at the meeting.
The coalition is widely derided as ineffectual by most regime opponents inside Syria, but the indications of rebel support may strengthen its hand, at least in the early stages. Diplomats have stressed that the talks are unlikely to produce a quick outcome, but rather will herald the start of what may turn into a long process of negotiations.