The Islamic State of Iraq and the Levant (ISIL) group has killed more than 100 civilians in a 24-hour rampage through the Kurdish town of Kobane in what a monitor group described as one of the group's "worst massacres" in Syria.

Women and children were among the slain civilians whose bodies were found in their homes and in the streets, the UK-based Syrian Observatory for Human Rights said.

"According to medical sources and Kobane residents, 120 civilians were executed by ISIL in their homes or killed by the group's rockets or snipers," Rami Abdelrahman, director of the Syrian Observatory, told AFP news agency on Friday.

"When they entered the town, the jihadists took up positions in buildings at the southeast and southwest entrances, firing at everything that moved."

"We heard gunshots at 5am. We went out to the street and saw people lying on the ground, shot and killed. Bodies and blood everywhere. Mahmoud Muslim, survivor

Turkish officials said more than 150 people were being treated in hospitals after crossing the border.

An explosion hit Kobane on Saturday, sending plumes of smoke into the air. The cause of the explosion was not immediately clear, said a Reuters news agency cameraman.

An unknown number of ISIL fighters were said to be holed up in at least four positions in Kobane - Mishta Nur hospital, a secondary school and two buildings near Rashad mosque - on Friday.

Kurdish officials said they were also holding at least 50 civilian hostages, using them as human shields.

The killing spree that started in the town, known as Ayn al-Arab in Arabic, on Thursday was widely seen as vengeance for a series of defeats inflicted on ISIL by Kurdish militia in recent weeks.

In January ISIL was forced to leave after months of fighting with Kurdish forces supported by US-led coalition air strikes.

Early on Thursday, dozens of ISIL fighters wearing uniforms of the YPG and the Syrian Free Army managed to enter the town.

They used suicide car bombers before fighters began randomly shooting at people.

"We heard gunshots at 5am. We went out to the street and saw people lying on the ground ... shot and killed... Bodies and blood everywhere," Mahmoud Muslim, who survived the attack, told Al Jazeera outside a hospital in the Turkish border town of Suruc.

"My father was shot. We kept moving from street to street to escape."

"The fighting is continuing but Kurdish officials say they are confident they will restore peace and security in their town which has been a symbol of Kurdish defiance," Al Jazeera's Zeina Khodr, reporting from southern Turkey, said.

"ISIL's intention may not be to capture Kobane but to send a message that it can't be defeated."

In an audio recording a few days ago, ISIL's spokesman Abu Mohammed al-Adnani said: "We may lose some battles but we won't be defeated."

The group has suffered a string of defeats at the hands of the Kurds in northeastern Syria - the most recent was in Tal Abyad, a strategic border town that ISIL used as a trade and smuggling route for foreign fighters and supplies

"They are taking revenge against us," Mohammed Hammu, a Syrian Kurdish activist, told Al Jazeera.

But Al Jazeera's Khodr said the assault may be more than just about revenge.

"It is clearly about instilling fear - and this unexpected and spectacular attack allows it to boast an achievement that is in line with its strategic message which is 'the caliphate remains'," she said.