MURSITPINAR, Turkey — The U.S.-led coalition ramped up its aerial bombardment of Islamic State positions in the Syrian border town of Kobani on Thursday as the extremist group battled street by street with Kurdish forces and reportedly rushed in reinforcements from surrounding areas.

The battle for the town near the Turkish border has emerged as a major early test for the U.S.-led air campaign aimed at rolling back and eventually destroying the extremist group, and has strained ties with NATO ally Turkey, which is at odds with Washington over its long-term strategy in Syria.

The U.S. Central Command said five airstrikes south of Kobani since Wednesday had destroyed an Islamic Stategroup support building and two vehicles, and damaged a training camp. The strikes also struck two groups ofIslamic State fighters, it said in a statement.