Idriss Nasan, speaking to CNN by phone from the Kurdish-held city in northern Syria, described a complex attack Thursday morning in which ISIS militants entered Kobani from the east and west in disguise.
"They were wearing YPG (Kurdish security forces) uniforms, so when people saw them they did not fear them, and they (ISIS) opened fire. Many civilians lost their lives," he said.
Eyewitnesses said some gunmen spoke Kurdish and knocked on doors telling locals to come out. "People rushed out and were killed," Nasan said.
ISIS fighters also attacked Syrian regime forces Thursday in the northeastern city of al-Hasakah, said the London-based Syrian Observatory for Human Rights.
Analysts said the dual offensive against Kobani and al-Hasakah might be an ISIS effort to divert Kurdish fighters away from Raqqa, ISIS' self-declared capital in Syria, where the terror group appeared to be bracing for a Kurdish attack.
In Kobani, only a few ISIS fighters remained holed up in a house at 2 p.m. Thursday, and the YPG was trying to capture or kill them, Nasan said. He said it was unclear how many ISIS militants were fighting or how many Kurdish civilians had died. ISIS detonated at least two bombs, one in a car and the other in a motorcycle, he said.
In the Kurdish village of Barkh Butan near Kobani, ISIS militants killed at least 20 people, including some who were "executed," according to the Syrian Observatory for Human Rights. Activists say ISIS has detonated up to three car bombs near the Syrian-Turkish border.
Kobani is a strategically valuable city that sits on the border with Turkey. ISIS took the city last fall after a brutal back-and-forth battle but abandoned it in January in the face of a Kurdish offensive backed by airstrikes by the U.S.-led international coalition.
Attack on al-Hasakah
In al-Hasakah, about 270 kilometers (170 miles) east of Kobani, heavy clashes were underway, the SOHR said, and the Syrian air force is conducting airstrikes in the area.
ISIS militants detonated at least one car bomb at a Syrian military checkpoint and have taken control of some neighborhoods in the southern part of the city, according to the group.
The SOHR reported at least 30 killed among regime forces and 20 dead from ISIS' ranks. CNN cannot independently confirm the casualty numbers.
These ISIS offensives come in the wake of recent losses by the terror group in the Syrian cities of Ain Issa and Tal Abyad in the ISIS stronghold province of Raqqa, where Kurdish forces, backed by U.S.-led coalition airstrikes, were able to beat back the militants.
Those tactical victories put ISIS' formidable rivals just 55 kilometers (about 35 miles) away from the city of Raqqa.
ISIS was reportedly digging trenches and calling on reinforcements
to prepare for a possible Kurdish assault on Raqqa, activists and a Kurdish official told CNN on Wednesday.
ISIS moved a convoy of nearly 100 military vehicles packed with arms, ammunition and fighters from the countryside east of Raqqa to one of the terror group's bases within the city, said Rami Abdelrahman, the director of the SOHR.
Analyst Charles Lister of the Brookings Doha Center said via Twitter that the latest ISIS offensive appeared to be "classic" ISIS strategy -- assaults on Kobani and al-Hasakah to divert the Kurds from Raqqa.
Lister added that reports ISIS fighters disguised themselves to gain entry to Kobani were an "important signal of intent: not just to divert but instill paranoia."
Natasha Underhill, an expert on terrorism in the Middle East at Nottingham Trent University, said recent ISIS retreats don't mean the group is weakening.
"(ISIS) is a very tactical and strategic group, much more-so than al-Qaeda ever were," she wrote in an email. "What we term strategic wins against (ISIS) may simply be the group withdrawing and re-strategising. This could be what we are seeing at the moment in (Kobani); the two-pronged approach used by the group in the re-taking of parts of (Kobani) show that this group is functioning more like an army than a terrorist organisation."
Islamists clash with Syrian regime forces near Daraa
In the south of Syria, an alliance of 51 Islamist rebel factions, including the al Qaeda affiliate Nusra Front, clashed with Syrian regime forces Thursday in Daraa, according to SOHR.
The monitoring group said it received a video statement from the alliance announcing the launch of a military operation named "Southern Storm" in an effort to drive out regime forces which control parts of the city of Daraa and surrounding areas.
SOHR said clashes are ongoing, but a leading Syrian newspaper, which leans editorially toward the regime, claimed the army repelled the rebel attack.
The Al-Watan newspaper on its Facebook page quoted the governor of Daraa as saying "the militants waged a real war using various weaponry on parts of the city but the army repelled their attack and the situation is now secure."
Official news agency SANA said government forces inflicted heavy losses on the "infidel terrorist groups" on the outskirts of Daraa.
Daraa, which is close to the Syrian-Jordanian border, is known as the "cradle of the revolution" because protests there in March 2011 helped spark Syria's Arab Spring uprising against the government.
At least one Jordanian was killed and several wounded when stray shells from the fighting in Daraa landed on the Jordanian side of the border, official sources told CNN.