A suicide bomber killed 29 people, most of them rebels, on Friday near the Syrian town of Al-Bab, which they had taken from the Islamic State group just hours earlier, a monitor said.
The bomber blew up a vehicle packed with explosives in Susian, eight kilometres (five miles) northeast of the strategic town which the Turkish-backed rebels overran on Thursday after weeks of fighting, the Syrian Observatory for Human Rights said.
The blast devastated two adjacent rebel command posts and also seriously wounded a large number of fighters, the Observatory said.
Al-Bab, just 25 kilometres (15 miles) south of the Turkish border, was the last IS stronghold in the northern Syrian province of Aleppo.
Rebels launched an offensive to capture the town last year with the support of Turkish ground troops, artillery and air strikes.
Turkey sent troops into Syria last August in an operation it said targeted not only IS but also US-backed Kurdish fighters whom it regards as terrorists.
The battle for Al-Bab has been the bloodiest of the campaign with at least 69 Turkish soldiers killed there.
Turkish Defence Minister Fikri Isik said on Thursday that its rebel allies had "near complete control" of the town.
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