Turkey's military said Wednesday that Syrian rebel forces with Turkish support have taken control of strategic hills surrounding the Islamic State-held town of al-Bab.
The Britain-based Syrian Observatory for Human Rights, which monitors the war in Syria, said Turkish forces and allied Syrian rebels launched an operation late Tuesday and seized territory on the western outskirts of al-Bab.
The town is a key area in northern Syria that increasingly is becoming a focal point of the multi-party conflict.
Syrian forces have advanced from the south to within about 3.5 kilometers of al-Bab, the Observatory says. Turkish and rebel fighters are coming from the north, while Syrian Kurds hold territory to the east and west. All of those groups have fought to push out Islamic State fighters, but what happens if the militants are routed from al-Bab remains a looming issue.
The Syrian government has long complained about Turkish activity in Syria, particularly since Turkey launched what it calls Operation Euphrates Shield in August. Turkish President Recep Tayyip Erdogan said the offensive was in response to a series of attacks in Turkey, and that he wanted to end threats from "terror" groups that included Islamic State and the Syrian Kurdish fighters.
Turkey sees the Syrian Kurds as aligned with Kurdistan Worker's Party, or PKK, rebels who have carried out a decades-long insurgency based in southeastern Turkey.
Syria last week sent letters to the United Nations again condemning Turkey's military actions, including the push toward al-Bab. The letters further accused Turkey of supporting terrorist organizations in Syria.
Turkey supports rebels who opposed Syrian President Bashar al-Assad, and Assad's government routinely refers to any opposition fighters as terrorists.
The many parties involved in the fighting have not made finding a resolution any easier. The United Nations is holding its next round of peace talks beginning February 20 in Geneva. A spokeswoman for U.N. envoy for Syria Staffan de Mistura said invitations for the talks were due to be sent on Wednesday.
The U.N. has sponsored several rounds of talks in recent years, but none have produced much progress in ending the fighting. The process has worked off a framework that calls for a total cease-fire and a Syrian-led political transition that includes a new constitution and elections.
Assad's future is not part of the outline, and disagreements about whether he should remain in power or leave have been one of the main sticking points in past negotiations.