BEIRUT (AP) — The Latest on the conflict in Syria (all times local):
Turkey says it may launch a cross-border operation into the Kurdish-controlled enclave of Afrin in northern Syria if it constitutes a "constant security threat."
Defense Minister Fikri Isik told state-run television TRT on Tuesday that Turkey's military will continue to respond to the "slightest fire" into Turkish territory from Afrin. He spoke hours after reports that Turkey's military retaliated overnight to fire from areas controlled by Syrian Kurdish groups.
Turkey considers the main Syrian Kurdish militia, which is supported by the United States, to be an extension of Kurdish rebels fighting in Turkey. The U.S. views the Syrian Kurds as the most effective ground force battling the Islamic State group in Syria.
Last year, Turkey sent troops into Syria to help Syrian opposition forces battling to oust Islamic State militants from another border region and to curb the territorial advances of the Syrian Kurdish militia.
Isik said: "We would not abstain from doing what is necessary if Afrin becomes a constant security threat."
The U.S. military says allied Syrian forces have breached the wall around Raqqa's Old City, where they are fighting to drive Islamic State militants from the extremists' self-declared capital.
Central Command said in a statement Monday that by punching through two "small portions" of the Rafiqah Wall they were able to enter the Old City while avoiding booby traps and IS snipers. It says the strikes left most of the 2,500-meter (yard) wall intact.
The Syrian Democratic Forces, a Kurdish-led militia, is battling IS in Raqqa with the help of U.S.-led airstrikes and U.S. special operations forces.
Several IS leaders were once based in Raqqa, where the group is believed to have plotted attacks in Europe. The loss of the northern Syrian city would deal a major blow to IS.