Thursday's fighting comes a day after the Islamic State of Iraq and the Levant (ISIL) was expelled from Aleppo city by rebels fighting to topple President Bashar al-Assad.
The rebels last week launched an all-out attack on the jihadist group.
While jihadists were initially welcomed in Syria by rebels battling Assad's forces, ISIL became hated because of its systematic abuses and its bid to dominate areas that have fallen out of regime control.
In a counterattack, ISIL launched car bomb assaults late Wednesday targeting opposition checkpoints, the Syrian Observatory for Human Rights said.
"At least nine people were killed in a car bomb attack by ISIL on a rebel checkpoint... in Al-Bab town" in Aleppo province, Observatory director Rami Abdel Rahman told AFP.
He said similar overnight attacks took place in Hreitan and Jarabulus in Aleppo province, and in Mayadeen in the eastern province of Deir Ezzor.
Early Thursday, the focus of the fighting was on Raqa, Idlib and Aleppo, the three main provinces of conflict between ISIL and rebels, the Observatory said.
"ISIL has sent reinforcements from Deir Ezzor to back its fighters in the Aleppo countryside," said Abdel Rahman, who relies on a network of activists on the ground for his reports.
"Residents say ISIL is preparing many suicide attacks in retaliation, and that their commanders wearing explosive belts all the time," he added.
In Raqa, where ISIL is headquartered, fighting raged between the jihadists and rebels on Thursday, the Britain-based Observatory said.
"The rebels have taken control of the strategic political intelligence building, which had been under ISIL control and is just 400 metres (yards) from the jihadists' headquarters," Abdel Rahman said.
"But ISIL still controls the bridges leading into the city, so people have to take boats to get in."
Raqa is Syria's only provincial capital to have fallen out of regime control.
Weeks after its takeover by rebels, ISIL moved in and has since been accused of imposing a reign of terror including kidnappings, torture and assassinating activists and rival rebels.