Syria's main Kurdish militia issued a call to arms to battle jihadists after a Kurdish leader was killed on Tuesday weeks into clashes between the minority group and radical Islamists.
It came as regime warplanes staged new air strikes in Aleppo, Homs and Idlib provinces, killing at least 16 children, the Syrian Observatory for Human Rights said.
A local official trying to broker peace between loyalists and insurgents was also killed by unidentified gunmen near Damascus, said the Observatory.
"We call on the Kurdish people... to step forward... anyone fit to bear arms should join the ranks of the Committees for the Protection of the Kurdish People (YPG) and to face the assaults of these (jihadist) armed groups," said a YPG statement published on a Kurdish website.
Isa Huso, a prominent Kurdish politician, was assassinated as he left his house in the city of Qamishli, a pro-Kurdish news agency reported.
That raised to new heights Kurdish resentment against the main opposition National Coalition and mainstream rebel Free Syrian Army (FSA).
"Despite our repeated calls to the National Coalition and the Free Syrian Army command... to date these parties have failed to take a clear position" against the radicals, the YPG statement said.
It said it was clear that FSA battalions were coordinating with jihadist groups.
It singled out Al-Nusra Front and the Islamic State of Iraq and the Levant (ISIS), saying they and the FSA "have become one side in attacking the Kurdish people".
A Kurdish politician and member of the Syrian National Council -- which is opposed to President Bashar al-Assad -- said the call to arms came as no surprise.
"These obscurantist groups (Al-Nusra and ISIS) are not focusing on Homs (in central Syria) or Damascus province, where there are open battles against the regime," Mohammed Mustafa told AFP via the Internet.
"Instead, they are assaulting areas that have fallen out of regime control and attacking the Kurds."
Opponents "accuse the Kurds of being pro-regime, when in fact it is the jihadists who are helping the regime and all those who want to see Syria's future destroyed," Mustafa added.
Clashes between jihadists and Kurdish fighters have raged for some two weeks, after jihadists were expelled from the key town of Ras al-Ain on the Turkish border.
Marginalised for decades by Damascus, Kurds and their fighters have tried to ensure that neither regime forces nor the opposition takes control of their areas.
On another front, warplanes raided rebel-held Anadan in the northern province of Aleppo, killing at least seven children and three women, said the Observatory.
Earlier, a family of seven, including four children, were killed in a raid after they fled the army's recapture of Khaldiyeh district in Homs city.
Also on Tuesday, explosive-laden barrels dropped from a helicopter onto Mantaf village in the northwestern province of Idlib killed 11 people, among them five children and four women, the Observatory said.
In Zabadani, near Damascus, gunmen killed Majed al-Tenawy, head of the local council who was mediating between rebels and troops, said the Observatory.
Fighting also raged on the eastern edges of Damascus near strategic Abbasiyeen Square, the group added, while troops shelled rebel positions in Jubar and Qaboon in the city's strife-torn eastern belt.
In Doha, opposition chief Ahmad Jarba said the Coalition will form a provisional government in the second half of August, after months of failed efforts.
"I expect a government in exile to be formed around 10 days after Eid al-Fitr," the holiday ending the Muslim fasting month of Ramadan that falls on August 8 or 9, he told AFP.
The opposition has struggled to put forward a united front during more than two years of conflict in Syria.
Jarba also said the opposition needs clarifications before deciding about proposed peace talks, including on the position of Russia, which is providing unwavering support to Assad's government.
He said the opposition was still keen to receive weapons to combat regime forces, "even while a political solution is sought through Geneva 2".
The Arab League and the Organisation of Islamic Cooperation both appealed to warring parties in Syria to observe a ceasefire during Eid al-Fitr.
Earlier this month, UN chief Ban Ki-moon urged a truce for Ramadan, although there was no response to his appeal.
A proposed Eid truce last year fell through.
The United Nations says that more than 100,000 people have been killed in the war which erupted in 2011 after a regime crackdown against anti-Assad dissent.