At least 14 civilians, most of which were children, were killed in regime attacks in de-escalation zone in northern Syria on Saturday, according to sources with the White Helmets civil defense agency.

Regime forces bombarded the town of Ariha in Idlib province and the towns of Al Amqiyah, Morek, Hawash and Al-Zeyarah in Hama province, the sources said.

The airstrike in Ariha left 14 people dead and 30 others injured. A three-year old girl with an amputated leg and a man with serious injuries to his bladder and torso were also among the injured, according to Dr. Mohamad Abrash, a surgeon and head of the Idlib central hospital. Both are in critical condition, he said.

The Syrian Observatory for Human Rights, which monitors the war, and another activist collective, called Ariha Today, said most of those killed were children. Ariha Today named six children under the age of 14 who it said were killed in the airstrike.

Ariha has been repeatedly targeted over the past week as Syria's regime looks to regain momentum in its stalled offensive, which began in late April. It is one of the main towns in Idlib province, which along with the surrounding rural areas of Hama province, are home to 3 million people.

Separately, local doctors said two medics and an ambulance driver were killed when an airstrike targeted their vehicle in Kfar Zita, a town on the frontline in Hama province, at the edge of the rebel stronghold.

Ghayath, an activist in Ariha who only gave his first name out of fears for his safety, said the strike hit the town during the busy weekly bazaar when people come to buy food and other necessities. He said the death toll could have been higher if it were not for the warning from the local civilian defense team against large gatherings.

"The strike hit the main square, in the center of town," he said.

"This is a systematic displacement policy to empty the busy town out," said Abrash, the doctor, who said the injured travel nearly five kilometers (3 miles) to reach Idlib city, which has the most well-equipped hospital for surgery.

Turkey and Russia agreed last September to turn Idlib into a de-escalation zone in which acts of aggression are expressly prohibited. The Syrian regime, however, has consistently broken the terms of the cease-fire, launching frequent attacks inside the de-escalation zone.

In the Syrian regime's airstrike campaign, backed by ally Russia, warplanes have targeted medical centers, water plants and residential areas, in what the U.N. and rights groups call a deliberate campaign that amounts to war crimes.

The rebel enclave is dominated by al-Qaida-linked militants and other extremist groups. The regime says it is targeting terrorist locations.

Most of the civilians living in the rebel stronghold have already been displaced by other bouts of violence, and have chosen not to live in regime-captured areas.

Over the last three years, the regime regained control of most of the territories that were initially seized by the opposition in the early days of the civil conflict — now in its 9th year.

Those military victories, backed by Russian airpower and Iranian-backed militias on the ground, followed intense military campaigns and tight sieges that forced those opposed to surrender and move north.

Last week, a residential building in Ariha was hit, killing a mother and two of her daughters, while two other girls are recovering in the hospital. The father survived the attack.

The U.N. human rights chief, Michelle Bachelet, said Friday that the world's most powerful nations are failing to show leadership in dealing with the Syrian crisis "resulting in a tragedy on such a vast scale that we no longer seem to be able to relate to it at all."

According to her office, at least 450 civilians were killed since the offensive began in April 30, including more than 100 in the last 10 days alone. More than 440,000 people were displaced inside the crowded enclave to escape the airstrikes.

Syria has only just begun to emerge from a devastating conflict that began in early 2011 when the Bashar Assad regime cracked down on demonstrators with unexpected severity.