Turkish President Recep Tayyip Erdogan on Thursday dismissed as "propaganda" accusations that Islamic State fighters had been allowed to cross from Turkey into Syria to launch a fresh assault on the symbolic battleground town of Kobane.
"We condemn the heinous attack by the terrorist IS organisation that targeted innocent civilians in the city of Kobane," Erdogan said in a speech.
Dozens of civilians and fighters on both sides were killed when the IS jihadists 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 IS militants passed through the Mursitpinar border crossing in Turkey to make their way into Kobane.
Describing those allegations as "defamation and propaganda", Erdogan said: "No one has the right to link Turkey to terrorist organisations".
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 IS militants.
Turkish officials meanwhile said four victims had died in Turkish hospitals while 135 wounded received treatment on the Turkish side of the border.
The Turkish government said video footage taken from Turkish border security units and broadcast by the state-run Anatolia news agency showed a bomb-laden car did not pass through the Turkish border crossing.
But Kurdish activists accused Turkey on social media of assisting the IS group, with the hashtag #TerroristTurkey becoming a trending topic on Twitter.
Arin Shekhmos, a Syrian Kurdish activist, told AFP in Beirut earlier that IS had entered Syria from Turkey through the Mursitpinar border crossing.
He claimed the IS forces were wearing Kurdish People's Protection Units (YPG) uniforms as a disguise when they entered.
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- 'Back and forth' -
The accusations come amid growing tensions between Syrian Kurds and Turkey.
Turkey says Syrian Kurdish forces who recently made gains in Syria against IS are linked to the Kurdistan Workers' Party (PKK), which for decades has waged a deadly insurgency inside Turkey.
Western states have repeatedly accused Turkey of not doing enough to halt the flow of jihadists in both directions across its 911-kilometre (566-mile) border with Syria.
Turkey fiercely rejects the accusations, saying it is making every effort to secure a long border and in turn has accused the West of not playing its part to shoulder the burden of hosting refugees from Syria.
But Turkey's opposition pro-Kurdish Peoples' Democratic Party (HDP) accused the authorities of long allowing IS fighters back and forth across the border.
"IS 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 IS is no longer using the border when it has been doing so for so long before," she added.
Kurdish forces backed by US-led air strikes and 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.