BEIRUT—The head of Syria´s main opposition coalition offered to resign, two days after his re-election sparked broad discontent among antigovernment activists, as hundreds of students clashed with pro- government forces.

The move on Thursday threw Syria´s fragmented opposition into further disarray, as frustration mounts among activists who say their political infighting has helped President Bashar al-Assad pursue an unfettered crackdown on dissent. The development was also likely to set back efforts to lure more Western aid, as foreign powers have cited the lack of cohesion by Syria´s dissidents as an impediment.

Kofi Annan, the United Nations and Arab League peace envoy to Syria, said he, too, was concerned the opposition was facing difficulties in uniting, his spokesman, Ahmad Fawzi, said.

Burhan Ghalioun, who has presided over the Syrian National Council since it was effectively formed in September, said he would step down once a new candidate was chosen.

His decision comes after months of mounting tensions and power struggles within the SNC, an umbrella group that has served as the opposition´s point of liaison with most Western and Arab governments.

Mr. Assad this week appeared to belittle the SNC in his first television interview since December. "I don´t think that they have any kind of weight or significance within Syria," he told a Russian state television channel, the Associated Press reported.

Meanwhile, hundreds of students protested at Aleppo University in the presence of U.N. observers who are in Syria to monitor the terms of the April 12 cease-fire. That came two weeks after an on-campus raid by security forces left four students dead and shut the university.

On Thursday, some activists said pro-regime students and regime forces attacked demonstrators, but it wasn´t clear whether the monitors witnessed the fight.

Mr. Ghalioun, a 67-year-old Paris-based academic, offered to resign after one of the earliest and broadest grassroots activist networks in the uprising, the Local Coordination Committees, threatened to pull out of the coalition.

That threat signals a widening divide between the opposition´s exiled leadership abroad, led by the SNC in Istanbul, and activists leading protests inside Syria, many who feel they are facing the brunt of the risk.

Many activists say the council has lost touch with the uprising on the ground, failed to meet protester pleas for humanitarian aid or arms and only in vain lobbied foreign governments for help to stem the bloodshed.

"The SNC doesn´t mean anything to me," a 33-year-old protester in Damascus, Syria´s capital, said by Skype. "They don´t own this revolution. If they can help us get to the end, fine. If not, we´ll get there anyway."

Some allege an outsize role for one of the SNC´s seven main political factions, the Muslim Brotherhood, whose backing for the secular and liberal Mr. Ghalioun has helped cement his leadership but has alienated other secular factions.

Samir Nachar, a member of the council´s top leadership committee, said the council now faced "a real crisis." Members met on Skype on Thursday evening to plan their next moves, he said.

Molham al-Droubi, a Brotherhood member on the council, said the group would have to restructure to become more inclusive to other opposition coalitions and recruit qualified technocrats from outside the council "who can do the job."

"If this happens, we will save the SNC," Mr. Droubi said by telephone. "Otherwise, I think the SNC will no longer exist."

He said the Syrian Muslim Brotherhood was aware of allegations it was monopolizing decision-making in the council, which he acknowledged but said was due to it superior organizational abilities. Brotherhood members had reached out to other opposition members and Western diplomats to address these concerns, he said.

A 10-member panel appointed in April to restructure the SNC´s leadership bodies and broaden the council failed to do so amid disagreements, panel members said.

But other activists warn that the bickering in the opposition is setting back efforts to form a united front against Mr. Assad, allowing him to defy the cease-fire.

On Tuesday, Mr. Ghalioun´s competitor in elections was George Sabra, a Christian whose candidacy was backed by another longtime opposition group called the Damascus Declaration.

Analysts and some activists say a council under Mr. Sabra would send an important message to Syria´s religious minorities in an uprising that has pitted the majority-Sunni protest movement—a reflection of Syria´s Sunni-majority population—against a regime dominated by Alawites, an offshoote Muslim sect associated with Shiism.

A version of this article appeared May 18, 2012, on page A9 in the U.S. edition of The Wall Street Journal, with the headline: Syrian Split Sets Back Bid to Unseat Assad. (Copyright © Dow Jones & Company, Inc.) 05/18/12)