BEIRUT -- An airstrike hit a busy market in a rebel-held town in northwestern Syria on Monday, killing at least 23 people, according to opposition activists and a war monitoring group.

The airstrike took place in the town of Maaret al-Numan and also wounded more than 30 people, according to the reports from the region which has witnessed intensive airstrikes and bombardment almost every day as Syrian troops, backed by Russian air cover, try to push their way into the enclave near the Turkish border.

Syrian state TV said insurgents shelled the government-held town of Suqailabiyah, wounding four people, including a child.

Idlib province, in the northwestern corner of Syria, is the last major rebel stronghold in the country outside the control of Syrian President Bashar Assad.

Syrian government forces launched their offensive in Idlib province in late April and fighting has killed more than 2,000 people and displaced hundreds of thousands.

But the troops have made little progress since the push started.

The Britain-based Syrian Observatory for Human Rights, which monitors the fighting on the ground in Syria through a network of activists, said 23 people were killed, including two children, in the strike on Maaret al-Numan. It added that the number of casualties from Monday's airstrike was likely to rise due to the large number of wounded.

The Thiqa news agency, an activist collective in northern Syria, gave a higher death toll, saying the strike killed 27 people.

A member of the Syrian Civil Defence, also known as White Helmets, said one of their colleagues was killed in a second airstrike that hit the market.

On Sunday, government bombing in Idlib killed at least 11 civilians according to the Observatory and first responders.

Despite the heavy bombardment, Assad's troops have been unable to make any significant advances against the rebels or the al-Qaida-linked militants and other jihadi groups who dominate Idlib province. Militant groups have hit back hard, killing an verage of more than a dozen soldiers and allied militiamen a day in recent weeks.

The struggling campaign underscores the limits of Syria's and Russia's airpower and inability to achieve a definitive victory in the country's long-running civil war, now in its ninth year.

In neighbouring Turkey, Foreign Minister Mevlut Cavusoglu said Ankara would launch a new offensive into northern Syria if a so-called "safe zone" is not established and if threats against Turkey continue from the region.

Cavusoglu made the comments on Monday as a delegation led by U.S. Special Representative on Syria, James Jeffrey, was to hold talks in Ankara. The possible safe zone along the border with Turkey was expected to be on the agenda.

Turkey views Kurdish fighters who have fought alongside the United States against the Islamic State group as terrorists and wants the safe zone established to keep the fighters away from the border. It has recently been sending troop reinforcement to its border region.

Cavusoglu said Turkey would intervene "if there's no safe zone and if the terrorists are not cleared and continue to pose a threat."

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Associated Press writer Suzan Fraser in Ankara, Turkey, contributed to this report.