Turkey's security forces closed the border with Syria through which thousands of Kurds are trying to flee IS, after clashes between Kurds and soldiers on the Turkish side of the divide.

The separatist Turkey-based Kurdistan Workers Party (PKK), which is classed as a terrorist organization by Istanbul, called for a solidarity demonstration on Sunday, after 70,000 Kurds crossed from Syria in just 24 hours.

Hundreds of Kurds duly showed up near the barbed wire border fence - some volunteering to join the struggle against IS, others asking to bring over aid to the refugees on the other side of the border.

Clarification: some ppl on Turkish side want to go in and get family, in some cases to fight #IS. Turks won't open the border until they go — Lizzie Phelan (@LizziePhelan) September 21, 2014

On 1 side Syrian #Kurds try 2 get thru on other Turkiah Kurds trying to convince authorities to let them in. V tense pic.twitter.com/7amnvDK9NB — Lizzie Phelan (@LizziePhelan) September 21, 2014

As was witnessed by RT's camera crew, Turkish border forces refused to let them pass, and as tensions mounted, attempted to disperse the rally with water cannons and gas grenades.

In turn, the Kurds set up barricades near the checkpoint, and began to throw stones at the uniformed troops.

Meanwhile, the border remained closed, meaning that thousands of refugees were unable to escape to safety, or obtain basic necessities.

The London-based Syrian Observatory for Human Rights said that more than 300 Kurdish fighters have crossed into Syria from Turkey lately.

Syrian Kurds have been fleeing to Turkey since Tuesday, when the Islamic State (IS, formerly known as ISIS) launched an offensive operation against Kurd-populated areas in the north of the country. The IS has captured at least 64 villages around the border city of Ayn al-Arab, which Kurds call Kobani.

Town of #Suruc on the border with Syria, everywhere you can see the mass exodus of people from Syria @Ruptlypic.twitter.com/WPj79jNiCM — Lizzie Phelan (@LizziePhelan) September 21, 2014

According to estimates by the UN’s refugee agency, at least 70,000 Kurds, most of them women, children and elderly people, have fled to Turkey since Saturday alone, and the total may be even higher.

"I don't think in the last three and a half years we have seen 100,000 cross in two days. So this is a bit of a measure of how this situation is unfolding, and the very deep fear people have about the circumstances inside Syria and for that matter, Iraq," Carol Batchelor, UNHCR's representative in Turkey said.

Earlier the IS attacked the Kurd territories in the north of Iraq, sending tens of thousands of civilians on the run for their lives. IS has set up a self-proclaimed Sunni caliphate that stretches from Syria to central Iraq, and has established a reign of terror, in an attempt to control huge areas with limited manpower.

A US-led coalition has attempted to counter IS with increasingly intense air strikes for the past month.