Government troops shelled rebel-held areas and clashed with anti-regime gunmen throughout Syria on Saturday despite an internationally mediated ceasefire, while rebels and Kurdish neighborhood guards fought a rare battle in the embattled city of Aleppo that left nearly two dozen people dead, activists said.

The new violence — coming a day after car bombs and clashes left 146 people dead, according to Israel Radio — casts further doubt on the chances that the four-day ceasefire will be a springboard for ending the 19-month conflict.

A rebel commander in Aleppo said Saturday that UN-Arab League envoy Lakhdar Brahimi’s ceasefire had failed.

“This is a failure for Brahimi. This initiative was dead before it started,” Abdel Jabbar al-Okaidi, the head of the Free Syrian Army military council in the northern city of Aleppo, told AFP by telephone.

Al-Okaidi put the blame squarely on the shoulders of President Bashar Assad’s regime and insisted that the rebels had not broken the ceasefire.

“I was on several fronts yesterday and the army did not stop shelling,” he said. “Our mission is to defend the people, it is not us who are attacking.”

The fighting in Aleppo’s predominantly Kurdish neighborhood of Ashrafieh late Friday occurred a day after rebels pushed into largely Kurdish and Christian areas that have been relatively quiet during the three-month battle for the city.

Kurds say the rebels had pledged to stay out of their neighborhoods. Kurdish groups have for the most part tried to steer a middle course in the conflict between the rebels and the Assad regime. Some figures have allied with the rebels, others with Assad, and others have remained neutral.

The Britain-based Syrian Observatory for Human Rights said 19 rebels and three Kurdish gunmen were killed in the clash that lasted several hours, the group said. A Kurdish official put the death toll at 10 Kurds, but had no figures for the rebels.

Mohieddine Sheik Ali, head of the Kurdish Yekiti party, told The Associated Press that the clashes broke out after rebels entered Ashrafieh, violating “a gentlemen’s agreement” not to go into Kurdish areas in Aleppo.

He said there are 100,000 Kurds in Ashrafieh and many in the nearby Sheik Maksoud area. Sheik Ali said tens of thousands of Arabs have also fled to these areas from the violence in other parts of Aleppo.

“Disagreements between our brothers in the (rebel) Free Syrian Army and the Kurdish Popular Defense Units” led the clashes, he said.

The Observatory said the clashes led to a wave of kidnappings between the two groups, but did not provide further details. Pro-government news websites also reported the clashes.

Kurds are the largest ethnic minority in Syria and make up around 10 to 15 percent of the country’s 23 million people. Most of them live in the northeaster Hasakeh province near the border with Turkey, but large neighborhoods in Aleppo as well as the capital Damascus are Kurdish-dominated.

After the anti-government uprising began in March last year, both the Syrian government and opposition forces began reaching out to the long-marginalized minority whose support could tip the balance in the conflict.

Kurds have long complained of neglect and discrimination. Assad’s government for years argued they are not Syrians, but Kurds who fled from Iraq or neighboring Turkey. But the Kurds are also leery of how they would fare in a Syria dominated by the large Sunni Arab rebel movement.

Early on in the revolt, Assad ceded ground on a major Kurdish demand, granting citizenship to some 200,000 who were registered as aliens before. Mindful of provoking the Kurds, security forces have refrained from using deadly force to put down protests in Kurdish regions, and residents say they have largely abandoned their posts there.

The opposition has also courted the Kurds, staging demonstrations in hopes of rallying the community against Assad. In June, Abdelbaset Sieda, a Kurd, was elected as head of the Syrian National Council, the main opposition group in exile.

The Kurds in turn took part in the anti-Assad protests staged every Friday, but carried their own flags and chanted their own slogans.

Kurdish fighters from the Kurdish Democratic Union Party, or PYD, now secure much of the northeast. The group is affiliated with the Kurdistan Workers Party, or PKK, rebels fighting for autonomy in the Kurdish-dominated southeast region of Turkey. Turkey’s support for the Syrian rebel movement is another point of tension between the mainstream opposition and the Kurds.

In other violence, the Observatory and the Local Coordination Committees reported shelling and shooting Saturday mostly in Aleppo, the eastern region of Deir el-Zour, Daraa to the south and suburbs of the capital Damascus.

Syria mediator Lakhdar Brahimi, the UN-Arab League envoy, had mediated a four-day ceasefire that began Friday to mark the Muslim feast of Eid al-Adha.

“The ceasefire collapsed nearly three hours after it went into effect,” said Rami Abdul-Rahman, who heads the Observatory. “The only difference is that the fighting is less widespread and regime has not been using its air force since the ceasefire began.”

Also Saturday, state-run Syrian TV reported that rebels violated the ceasefire by detonating a car bomb outside an Assyrian Christian church in the eastern city of Deir el-Zour near the border with Iraq.

A Syrian official, who spoke on condition of anonymity in line with regulations, said part of the church was damaged but the blast caused no casualties.