A car bomb has exploded near a school in Syria, killing at least 18 people and wounding dozens more, according to a monitoring group.

The UK-based Syrian Observatory for Human Rights reported Thursday that the explosion took place in the village of Al-Kaffat, which is in the central Hama province.

The explosion comes as clashes continue between Syrian rebels and al-Qaeda-linked fighters in several northern towns.

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Opposition fighters on Wednesday stormed the town of al-Dana, a stronghold of the Islamic State of Iraq and the Levant (ISIL) in Idlib, as fighting continued in al-Bab and three other towns in Aleppo province, Al Jazeera’s correspondent in Aleppo said.

Since last week, a broad coalition of moderates and Islamists opposed to President Bashar al-Assad have been seeking to drive ISIL - which is accused of kidnapping, torturing and killing rival rebels and civilians - from its strongholds in the north and east of Syria.

Three powerful rebel alliances launched what activists called a second "revolution", and have advanced quickly, expelling ISIL from checkpoints and bases across Aleppo, Idlib and Hama provinces.

Several rebel groups seized the headquarters of ISIL on Wednesday.

The rebel-on-rebel clashes that erupted last Friday has killed more than 300 people, the UK-based Syrian Observatory for Human Rights said.

On Wednesday evening, activists said that ISIL, whose leadership is based in Iraq and members are mainly foreigners, detonated two car bombs near checkpoints manned by Syrian rebels in al-Bab, killing several people.

'Legitimate targets'

The blast came a day after ISIL urged people to target those who opposed them, including members of the Free Syrian Army and the main political opposition bloc, the Syrian National Coalition.

"All their members are legitimate targets. We have placed rewards on their heads. Kill them wherever they are found,” ISIL spokesman Abu Mohamed al Adnani said.

While rebels have been making swift victories in their battle against ISIL, the movement to remove Assad from power remains in disarray.

On Thursday, clashes continued between opposition fighters and Assad troops in several towns near Damascus and in the southern Deraa province.

In Latakia, government warplanes carried out an airstrike in Latakia province, activists said.

In amateur video footage uploaded on the internet, helicopters can be seen flying overhead during the bombardment and the man filming accuses them of the attack.

Syrian government has been accused of dropping barrel bombs onto heavily populated areas from helicopters.

More than 120,000 people have been killed in the nearly three-year conflict.

Source: Al Jazeera and agencies