Turkey shelled Kurdish fighters in Syria for a third day Monday and a suspected Russian air strike on a hospital left several dead, as violence shook the country ahead of a hoped-for ceasefire.

Ankara and Moscow also traded accusations over their respective roles in Syria, escalating a war of words that has dampened hopes that a proposed cessation of hostilities will take hold this week.

The cross-border Turkish artillery fire, which began on Saturday, comes amid deep concern in Ankara over advances by Kurdish-led forces in Syria's Aleppo province.

Turkey accuses the Kurdish forces of links to the Kurdistan Workers Party (PKK), an outlawed movement that waged a decades-long insurgency against the Turkish state.

Following similar fire on Saturday and Sunday, Turkish shelling again hit several parts of Aleppo province on Monday, according to the Syrian Observatory for Human Rights, a Britain-based monitoring group.

An AFP journalist on the Turkish border said Turkish howitzers opened fire on Monday afternoon for around 20 minutes from the Akcabaglar region near a border crossing with Syria.

The Observatory said the shelling hit areas including a road west of the town of Tal Rifaat, where the coalition of Kurdish and Arab fighters known as the Syrian Democratic Forces (SDF) has launched an assault.

The town, only 20 kilometres (12 miles) from the Turkish border, is held by an alliance of mostly Islamist rebels and one of their few remaining bastions in the area.

The shelling killed at least two children in the area on Monday, the Observatory said.

- Warning to Kurds -

The SDF was advancing despite the shelling, it said, and there was heavy fighting inside the western limits of Tal Rifaat.

The SDF has already seized the nearby Minnigh airbase from rebel forces, and severed the road between Tal Rifaat and the key rebel-held town of Azaz on the border with Turkey.

Turkey fears the Kurds will be able to create a contiguous Kurdish territory just across the border in northern Syria.

Turkey's Prime Minister Ahmet Davutoglu warned Monday that Ankara "will not let Azaz fall" to the SDF, adding "the necessary intervention will be made".

The situation is a major headache for Washington, which has backed the Kurds in their battles against the Islamic State group despite the discomfort of fellow NATO member Turkey.

In recent days, Washington warned the Kurds not to "take advantage" of the situation in Aleppo to seize new territory.

Turkey is also a key member of the US-led coalition fighting IS in Syria, and is allowing coalition planes to fly sorties from its Incerlik base.

Ankara's shelling has prompted criticism from Damascus, which has urged the UN Security Council to take action.

Turkey on Monday also denied claims it had sent troops into northern Syria and rejected reports it was planning a ground intervention.

In northwestern Idlib province meanwhile, suspected Russian strikes hit an MSF-supported hospital, the Observatory said.

MSF confirmed the hospital's destruction, without saying who was behind it, and reported at least seven people had been killed, with another eight staff members missing, presumed dead.

It said the dead were five patients, a caretaker and a guard, and added that an unknown number of patients were also missing.

- Hospital in ruins -

Russia began strikes in support of ally President Bashar al-Assad in September.

It says the strikes target the Islamic State group and other "terrorists," but rights groups accuse it of killing a disproportionate number of civilians.

AFP photos of the hospital showed it had partially collapsed in the attack. The surrounding area was strewn with twisted metal, cinderblocks and detritus from the damaged building.

"The destruction of the hospital leaves the local population of around 40,000 people without access to medical services in an active zone of conflict," said MSF Syria operations chief Massimiliano Rebaudengo.

The Observatory also reported 10 civilians, including three children, were killed in suspected Russian strikes in Azaz and an area nearby.

The strikes in Azaz hit by a hospital, the monitor said.

The Russian strikes have allowed government troops to press a major operation in Aleppo that has virtually encircled rebels in the east of Aleppo city, as well as pushing them from much of the region north of the city.

They have angered Turkey, with Davutoglu on Monday issuing Russia a stark warning.

"If Russia continues behaving like a terrorist organisation and forcing civilians to flee, we will deliver an extremely decisive response," he said.

His comments escalated a war of words with Moscow, which earlier criticised Turkey's shelling in Syria as "provocative" and said it backed raising the issue at the UN Security Council.

More than 260,000 people have been killed in Syria since the conflict began with anti-government protests in March 2011.