ANKARA: Turkish forces swept into Syria overnight to rescue about 40 soldiers who had been surrounded for months by ISIS militants while guarding the tomb of a revered Turkish figure.

Damascus described the operation as an act of “flagrant aggression” and said it would hold Ankara responsible for the repercussions.

The action, which involved tanks, drones and reconnaissance planes as well as several hundred ground troops, was the first incursion by Turkish troops into Syria since the start of the war.

The military said no clashes took place during the operation although one soldier was killed in an accident.

The 38 soldiers who had been guarding the tomb of Suleyman Shah, grandfather of the founder of the Ottoman Empire, were brought safely home.

Normally, the detachment is rotated every six months but the last one was trapped for eight months by ISIS fighters.

The tomb, on a site within Syria that Ankara considers sovereign territory as agreed in a 1921 treaty, was to be relocated close to the Turkish border, while Suleyman Shah’s remains were taken to Turkey.

“The remains of Suleyman Shah, along with ancestral relics, have been brought back to our country pending their temporary transfer to a new site in Syria,” said Prime Minister Ahmet Davutoglu.

He told a news conference that nearly 600 soldiers, including special forces commandos, took part in the mission. Turkey had not sought permission or assistance but had informed allies in the coalition against ISIS once it began.

“This was an extremely successful operation with no loss to our rights under international law,” said Davutoglu, flanked by the chief of the military and the defense minister.

The Syrian government said in a statement that Turkey would be held responsible for its violation of the 1921 treaty after failing to wait for an agreement from Damascus before proceeding.

The Turkish government had informed the Syrian consulate in Istanbul about the operation but had not waited for approval from Syria in a violation of the 1921 accord, it said.

“There will be a letter from the Foreign Ministry to the relevant parties in the [U.N.] Security Council,” Syrian Tourism Minister Bisher Yazagi told Reuters.

A Turkish security source said the operation was conducted via the Syrian Kurdish border town of Ain al-Arab with the support of local Kurdish authorities.

The Syrian government statement said the fact that ISIS militants had not attacked the tomb “confirmed the depth of the ties between the Turkish government and this terrorist organization.” Davutoglu said the tomb would be returned to its previous location once conditions allowed. He said the remaining buildings at the original site were destroyed to prevent their use after the remains were removed.

Elsewhere, an improvement in weather conditions allowed regime aircraft to pound rebel-held positions around the country with over 100 air attacks, according to the Britain-based Syrian Observatory for Human Rights.

It said Sunday 80 of the 117 airstrikes, which killed 35 civilians over the last 24 hours, involved barrel bombs dropped by helicopter. The crude devices were dropped on areas of Qunaitra province which borders Israel, the Observatory said, although no information about casualties was available.

In the north, rebel groups managed to effectively end a weeklong regime offensive north of Aleppo by reopening the road between the northern city and the Turkish border, the Observatory said.

It said some 150 regime fighters were killed in the campaign, although rebel groups have claimed double that number of fatalities, and said the “overwhelming majority” were inexperienced troops who had been snapped up for their compulsory service in recent months.

The stall in the offensive came as opposition activists and rebel groups accused the regime of committing a massacre in one of the several villages they briefly overran.

The Observatory said 10 children and 13 rebels were among 48 people executed by government forces in the village of Ratyan.

Abdel-Rahman said all the dead were from six families.

“There was no resistance except in one house where a rebel opened fire at troops before being executed along with his family.”

The Observatory added that 116 rebels, including a Nusra Front commander, were killed in the clashes.