Turkish and Syrian troops traded fire in northwest Syria on Monday, with more than 20 reported dead, further raising tension between Ankara and regime ally Moscow over the rebel enclave in war-torn Idlib. Russian air strikes also killed 14 civilians in the same area, where a government offensive has caused one of the worst displacement of the nine-year-old Syrian conflict, a monitoring group said.

The tit-for-tat shelling between Turkish and Russian-backed Syrian forces was the deadliest since Turkey deployed troops in Syria in 2016 and escalated tensions between the conflict's two top foreign protagonists.

Turkish President Recep Tayyip Erdogan offered rare criticism of Russia last week, accusing it of "not honouring" agreements to prevent a regime offensive on rebel-held Idlib.

The overnight clash began with regime shelling of Turkish positions in Idlib, hours after a Turkish military convoy of at least 240 vehicles entered northwest Syria, according to the Syrian Observatory for Human Rights, a Britain-based war monitor.

The attack killed five soldiers and three Turkish civilians despite previous coordination on where Ankara's forces would be, Turkey's defence ministry said.

The Russian defence ministry said Ankara had failed to give prior warning of its troop movements at the time of the incident.

Retaliatory rocket attacks by Ankara on regime positions later killed at least 13 Syrian government troops and wounded 20 others in Idlib and neighbouring Hama and Latakia provinces, the Observatory said. The heaviest Syrian casualties were inflicted south of Saraqeb, a flashpoint Idlib town that Damascus has been trying to encircle since last week, said the Observatory.

State news agency SANA said the Syrian army had not suffered any casualties.

Children killed

Speaking to reporters at an Istanbul airport before leaving for Ukraine, Erdogan said the counterattack that had targeted 40 locations.

He called on regime ally Russia to assume its "obligations" under previously signed agreements.

The Observatory said a new Turkish military convoy entered Syria on Monday.

Increasing attacks by the regime and Moscow in northwest Syria have displaced more than 388,000 people since December, according to the United Nations, forcing many of them towards Turkey's border.

Ankara - which already hosts more than three million Syrian refugees on its soil - says it fears the latest fighting will trigger another mass influx.

UN Secretary-General Antonio Guterres on Saturday called for an end to fighting in and around Idlib but air strikes, many of them carried out by Russian warplanes, have continued.

On Monday, Russian air strikes killed 14 civilians in northwest Syria, said the Observatory.

Nine of those killed were displaced people who died when a missile hit their car in the Urum al-Kubra area, on the rebel bastion's eastern flank.

An AFP reporter saw rescue workers carry away the limp bodies of two small children and lay them in blankets on the back of a pickup truck.

The regime now controls more than two thirds of Syria, up from a barely a fifth before Russia's military might came to the rescue in 2015.

A jihadist group led by members of Syria's former Al-Qaeda affiliate still controls swathes of land in and around Idlib province, which is home to some three million people and where pro-Ankara rebel groups are also present.

In recent weeks, pro-Damascus fighters have pressed northwards along the M5 highway that connects the capital to Syria's second city Aleppo, crossing Idlib.