BEIRUT — A suspected Islamic State car bomb killed at least 60 people outside the northern Syrian town of al-Bab, a day after rebels backed by Turkey pushed out militants to gain a potentially strategic foothold. But the blast showed the possible challenges in holding the gains by rebels seeking to cut off critical Islamic State supply routes to areas including the militants’ de facto capital, Raqqa. On another front, Iraqi warplanes carried out their first airstrikes in Syria targeting suspected Islamic State sites, Iraq’s prime minister, Haider al-Abadi, said in a statement. Today's WorldView What's most important from where the world meets Washington Please provide a valid email address. It said the attacks targeted Bukamal near the Iraqi border in response to recent bombings in Baghdad claimed by the Islamic State. It marked the first publicly acknowledged airstrikes in Syria by Iraq’s military, which has also been leading battles seeking to drive the Islamic State from its last strongholds in the northern Iraqi city of Mosul. About six miles northwest of al-Bab, witnesses said a pickup truck exploded outside a building in the village of Sousyan, where rebels were distributing permits for displaced residents to return. Turkey's state news agency Anadolu put the death toll at 60, while a local doctor said that figure was expected to rise. [Pentagon wants talks with Russia over Syria, Iraq air attacks] Images from the area showed blood and body parts littering the ground. “It drove right into the heart of the crowd. There were bodies everywhere; some of them were on fire. When I got closer to them, I realized I knew their faces. They were trying to go home,” said Khalil Abdulrahman, a Syrian journalist from al-Bab. The attack came a day after Turkey-backed Free Syrian Army rebels recaptured the town, pushing the Islamic State from its final foothold along Syria’s northern border with Turkey. The offensive, which began in early December, was long and bloody despite the backing of Turkish warplanes, tanks and special forces. There are fears that the Islamic State will not retreat without a fight. Last month, the extremist group killed 48 people with a blast in a busy marketplace in the northern town of Azaz, three years after rebel forces recaptured the area. “The situation in al-Bab is not stable,” Issa Khider, a local activist, said Friday. “ISIS dug trenches and tunnels all around this town, so everything on top of them is very weak. There are mines here that explode if you accidentally touch the hidden wire,” he said. The fighting has reduced much of al-Bab to a ghost town, its prewar population of about 100,000 having dwindled to the low thousands. Questions hang over where the Turkey-backed force will head next. Ankara’s military intervention last August complicated its relationship with the United States, which has backed a Kurdish-led force as its main spear against the Islamic State in Syria. Turkey views Syria’s Kurdish fighters as terrorists and is now pushing to send its own forces to recapture Raqqa. A memorandum signed late last month by President Trump ordered the Pentagon and other national security agencies to draft a new proposal by late February for the defeat of the Islamic State in Syria and Iraq. Turkey has proposed several different versions of a plan to take Raqqa, all of which involve Turkish troops, more U.S. personnel and Syrian Arab fighters. Zakaria Zakaria in Istanbul and Brian Murphy in Washington contributed to this report.