Dozens of civilians and Kurdish fighters were killed when the IS terrorists made a surprise return to Kobane on Thursday, detonating a suicide car bomb near the border and battling Kurdish fighters in the city. Two more bombs exploded later in the day.
Claims circulating on the Internet suggested several cars loaded with ISIS militants passed through the Mursitpinar border crossing in Turkey to make their way into Kobane.
The Syrian Observatory for Human Rights said at least 35 civilians and Kurdish fighters were killed in the car bomb and subsequent fighting in the centre and south of the town, along with 22 ISIS militants.
Four victims had died in Turkish hospitals and 135 wounded received treatment on the Turkish side of the border.
Kurdish activists accused Turkey on social media of assisting the ISIS group, with the hashtag #TerroristTurkey becoming a trending topic on Twitter.
Arin Shekhmos, a Syrian Kurdish activist, told AFP in Beirut earlier that ISIS had entered Syria from Turkey through the Mursitpinar border crossing.
He claimed the ISIS forces were wearing Kurdish People's Protection Units (YPG) uniforms as a disguise when they entered.
Many states have repeatedly accused Turkey of not doing enough to halt the flow of terrorists in both directions across its 911-kilometre (566-mile) border with Syria.
Turkey's opposition pro-Kurdish Peoples' Democratic Party (HDP) accused the authorities of long allowing ISIS fighters back and forth across the border.
"ISIS has in every period being using the Turkish border. It's been going back and forth. There's lots of proof of this," HDP co-chair Figen Yuksekdag said.
"It's not logical to think that ISIS is no longer using the border when it has been doing so for so long before," she added.
Kurdish forces backed by peshmerga fighters from Iraq scored a major victory in January by winning a hugely symbolic battle for Kobane.
Months of fighting has prompted a mass exodus of local residents, with some 200,000 fleeing across the border into Turkey.
Some 35,000 Syrians returned home after Kobane's liberation, another Turkish official told AFP.The official added that the border crossing of Mursitpinar that lies opposite Kobane has remained closed except for limited use by civilians returning after January.
He also said there was no sign of any new refugee influx so far.