BEIRUT -- Syrian protesters pelted a group of rival opposition leaders with eggs Wednesday outside Arab League headquarters in Cairo, accusing them of playing along with President Bashar Assad's government instead of working to overthrow the regime.

The attack highlights the growing fault lines in the Syrian opposition, which is struggling to overcome infighting in the face of a brutal government crackdown that has persisted even after Damascus agreed last week to an Arab League plan to stop the violence. Security forces killed at least 13 protesters nationwide Wednesday, activists said.

The two major opposition groups, the National Coordination Committee and the Syria National Council, are divided over issues at the core of the 8-month-old revolution, including whether to request foreign military assistance and accept dialogue with the regime. The divisions have prevented the opposition from gaining the traction it needs to present a credible alternative to the regime.

On Wednesday, around 100 protesters in Cairo threw eggs and tomatoes at a four-man delegation from the NCC as the group tried to enter the Arab League's headquarters for a meeting. Critics say the NCC, which includes veteran activists and former political prisoners, is far too lenient and willing to engage in dialogue with the regime.

The NCC's stance has prompted some anti-government protesters in Syria to carry banners reading: "The National Coordination Committee does not represent me."

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"What happened today in Cairo is a sign of the Syrian street's disenchantment with the NCC and its direction, which goes against the people's will," said Ausama Monajed, a London-based member of the Syrian National Council. "There should be no dialogue with this regime. Not before, nor after it withdraws its tanks from the streets."

Members of the NCC delegation, who also were shoved and taunted with shouts of "traitor!" were forced to turn back Wednesday but the head of the delegation, Hassan Abdul-Azim, managed to enter the Arab League's building from another entrance and met with Secretary General Nabil Elaraby.

Abdul-Azim described the accusations that his group was cooperating with the Syrian regime as "nonsense."

"We are a patriotic opposition ... and we reject excluding any group, but others want to exclude us because we reject the foreign intervention in Syria," he told reporters following the meeting with Elaraby.

Elaraby denounced the attack and said the Arab League is open for all Syrian opposition groups.

"What happened in Cairo is completely unacceptable behavior," Sada Hamzeh, a Paris-based Syrian dissident who is a member of the NCC, told The Associated Press.

She suggested supporters of the Syrian National Council were behind the attack, adding: "It's like everyone who is outside the Council is a traitor, it is another kind of dictatorship."

As the opposition struggles to find a unified voice, the government crackdown has continued.

Syria agreed to a peace plan brokered by the Arab League last week, but officials say Damascus has since failed to abide by its commitments to pull tanks and other armor out of cities and stop the bloodshed that the U.N. estimates has killed 3,500 people.

The deal also includes a pledge to work on starting a dialogue with the Syrian opposition.

The Arab League called an emergency meeting Saturday to discuss Damascus' failure to abide by its commitments.

It was not clear what action the league would take if the bloodshed continues, although it could isolate Syria by suspending or freezing its membership. That would be a major symbolic blow to a nation that prides itself on being a powerhouse of Arab nationalism.

Also Wednesday, the British-based Syrian Observatory for Human Rights and the Local Coordination Committees, key activist networks, said at least 13 people -- and possibly more than 20 -- were killed by security forces in Damascus, Homs and other cities, activists said.

The unclear death tolls point to the confusion in the aftermath of attacks in a country that has prevented independent reporting.

Most foreign journalists have been banned from Syria and local media are heavily restricted, making it nearly impossible to independently confirm events on the ground. Key sources of information are witness accounts and details gathered by activist groups.