The Kobani strike was part of a multi-pronged Islamic state offensive targeting Kurdish-dominated areas of northeastern Syria. The militants also struck the city of Hasakeh, jointly controlled by government forces and the Kurdish militia known as the YPG.
The fighting in Kobani left at least 35 dead and 55 wounded, according to the Syrian Observatory for Human Rights, a pro-opposition British-based monitor with a network of activists in Syria.
The Islamic State offensive was seen as a bid to blunt the advance of Kurdish-led forces toward Raqqa, the militant group's de facto capital in Syria. The militants launched their attack on Kobani with a car bomb near the Mursitpinar border crossing into Turkey, killing about 12 civilians, Ocalan Isso, deputy defense minister of Kobani, said in a phone interview.
In the ensuing chaos, the group's militants, disguised as YPG fighters, infiltrated the town, also known as Ayn Al-Arab, and commandeered a school, tossing hand grenades and deploying snipers on the roof, Isso said. But he said Kurdish forces had surrounded the building and that the Islamic State fighters were cut off from any reinforcements.
No official casualty figures were released, but Kurdish activists uploaded dozens of images on social media depicting the civilians killed and wounded in the violence. They also reported two other car bombs were detonated later in the day, while clashes continued in eastern parts of the city.
The Islamic State militants also overran the village of Barkh Botan, about 20 miles south of Kobani, killing at least 20 civilians and wounding 15 others, the Syrian Observatory for Human Rights said.
The Syrian state news agency SANA reported fierce clashes in Hasakeh, with government troops battling an Islamic State incursion in a western neighborhood. No casualty figures were provided, but the pro-Islamic State Aamaq News Agency claimed that about 70 soldiers were killed in the attacks.
Activists reported thousands of civilians had abandoned their homes and fled the fighting.
The latest Islamic State offensive raised new tensions about the role of Turkey, which fears the Kurdish offensive just across the border in Syria could fan separatist sentiment among its own Kurdish minority. Turkey views the YPG as a proxy for the Kurdistan Workers' Party, which waged a decades-long insurgency against the Turkish state.
Isso accused Turkey of being complicit in the attack on Kobani, charging that Islamic State fighters entered Kobani from Turkish territory. Turkish officials dismissed that claim, saying they possessed "concrete evidence that there was no crossing from the Turkish side," according to Agence France-Presse.
Last week, Kurdish-led forces routed Islamic State fighters who almost a year earlier had seized the border town of Tal Abyad. That offensive, backed by coalition airstrikes, cut off the Islamic State's main supply route to Raqqa, some 50 miles south. It also gave Kurdish forces an opportunity to consolidate two areas in northeastern Syria under their control, as well as opening up a corridor to Iraqi Kurdistan.
Elsewhere in Syria, 51 rebel factions operating in the southern province of Daraa announced a campaign to wrest control of areas of Daraa city from the government. SANA reported that an attack by "terrorists" -- the government's standard description of rebel factions -- had been thwarted, with fighter jets pounding rebel targets in surrounding villages.
The news agency also denied that the rebels had taken control of the strategic Daraa-Damascus road, one of two main highways linking southern Syria to Damascus, the capital and seat of power of President Bashar Assad.
The rebel operation, dubbed "Southern Storm," was spearheaded by factions associated with the Southern Front, a coalition of so-called moderate fighters. If successful, it would grant the rebels a rear supply base to mount operations on Damascus, a scant 59 miles north, as well as creating a contiguous zone of rebel control stretching from Kuneitra province, bordering the Israeli-held Golan Heights, to the outskirts of the Druze city of Suweida.
The Syrian Observatory put the death toll at 14 on the rebel side but did not give casualty figures for civilians or government forces.
The battle for Daraa city comes after a recent string of important gains for the Southern Front. Opposition activists claim the battlefield successes are the result of an intense three-month period of supply and armament for the coalition from a logistics hub located in the Jordanian capital Amman, staffed by operatives from a number of intelligence services, including the CIA.