Turkish soldiers launched an overnight mission into neighboring Syria, evacuating dozens of besieged troops guarding an Ottoman tomb and moving the crypt Sunday back to Turkey after ceremonially planting the country's crescent-and-star flag.

The mission, saving Turkish soldiers reportedly stuck for months at the tomb of the grandfather of the founder of the Ottoman Empire, saw hundreds of troops backed by tanks cross the border near the frontier town of Kobani once besieged by the Islamic State group.

Turkey was widely criticized for not intervening for months in the Kobani battle, which finally saw Kurdish fighters backed by U.S.-led airstrikes push out the extremists.

We had given the Turkish armed forces a directive to protect our spiritual values and the safety of our armed forces personnel," Prime Minister Ahmet Davutoglu said in televised remarks.

Nearly 600 Turkish soldiers on some 100 tanks and armored personnel carriers crossed into Syria on Saturday night, as drones and airplanes flew reconnaissance missions overhead, Davutoglu said Sunday.

One group traveled to the tomb, some 22 miles from Turkey on the banks of the Euphrates River in Syria's embattled Aleppo province, he said. Another group seized an area only 200 meters (yards) from the Turkish border in Syria's Ashma region to be the new home for the tomb, according to a statement from President Recep Tayyip Erdogan's office.

One soldier was killed in an "accident" during the operation, Turkey's military said, without elaborating.

Turkish media later showed nationalistic images of three Turkish soldiers raising the country's flag at the new site.

"Before the Turkish flag was lowered at (the tomb), the Turkish flag started to be waved at another location in Syria," Davutoglu said. He said troops destroyed the complex once housing the tomb.

The U.S.-led coalition forces were informed of the Turkish operation after its launch to prevent any casualties, Davutoglu said. U.S. officials offered no immediate comment.

Syria's Foreign Ministry denounced the Turkish operation, calling it a "flagrant aggression." In a statement carried by the state news agency, it also suggested that the mission indicated a close relationship between Turkey and IS. Syria routinely accuses Turkey of supporting the Islamic State group.

The ministry said Ankara informed the Syrian Consulate in Istanbul ahead of the operation but did not wait for approval from Damascus.

Turkey's foreign minister, Mevlut Cavusoglu, confirmed that Ankara had notified Syria before the operation that it was vacating the tomb temporarily, and that it would return to the area when it is "ready" to do so.

"We got permission from no one, we conducted it with our own initiative," he said.

There had been rumors for months that the soldiers stationed at the tomb had been besieged by militants from the Islamic State group, which hold a third of Syria and neighboring Iraq in their self-declared caliphate. Some 40 Turkish soldiers once guarded the tomb, making them a target for the Islamic State group and other militants in Syria's long-running civil war, though the overnight operation apparently saw no fighting.

The tomb belonged to Suleyman Shah, the grandfather of Osman I, founder of the Ottoman Empire. The site along the Euphrates River is revered by Turkey, a strongly nationalist country whose rights there stem from a 1921 treaty with France, then the colonial power in Syria. The Ottoman Empire collapsed in the early 20th century after World War I.

In the 1970s, Turkey moved the mausoleum to its last location because the old site at a castle further south in Syria was to be inundated by the waters of a new dam.

Shah, a Turkic leader, is believed to have drowned in the Euphrates in the 13th century. His followers headed north into what is today Turkey, where they launched the Ottoman Empire. Some historians question official accounts about the Shah's tomb, saying they might have been retrospectively concocted to enrich an imperial identity for Turks.

Turkey has wanted Syrian President Bashar Assad overthrown and has backed some rebels fighting against him. Earlier this week, Turkey signed an agreement with the U.S. to train and arm Syrian rebels fighting the Islamic State group.

With its 750-mile border with Syria, Turkey could be a major player in the fight against the Islamic State group. But negotiations with the U.S. over what to do about the Islamic militants have been fraught with disagreement — with Turkey insisting that the coalition needs to also target the Assad government.

Turkey also has had concerns over some of the Kurdish fighters battling the Islamic State group in Kobani. It views the Kurds fighting in Syria as an extension of the Kurdistan Worker's Party, which has waged a 30-year insurgency against the Turkish government and is designated as a terrorist group by the U.S. and NATO.