CORRECTION, 15/04/2016: A previous version of this story identified the spokesperson of the High Negotiations Committee as Salim Mesut. His name is Salim al-Muslet.

At least 30,000 civilians have fled camps for displaced people in northern Syria after they were overrun by the Islamic State of Iraq and the Levant (ISIL), according to Human Rights Watch.

The US-based rights group urged Turkey to open its border to the civilians fleeing fighting between ISIL, also known and ISIS, and opposition rebels.

Human Rights Watch also accused Turkish border guards of shooting at some of those displaced in Aleppo province as they approached the frontier.

Turkey has denied the accusation.

"Civilians were trying to flee but some were met with gunfire or told they would not be able to enter," Nadim Houry, deputy director of Human Rights Watch Middle East and North Africa division, told Al Jazeera from Beirut in neighbouring Lebanon on Friday.

"Those people need to be allowed with safety. The whole world is talking about fighting ISIS, and yet people who are escaping them are not welcomed anywhere."

Turkey allows Syrians who are in urgent need of medical care to enter the country.

A senior Turkish official denied the claims of border guards opening fire at refugees.

The official told Al Jazeera that sometimes smugglers and armed men infiltrate groups of refugees, so they are firing at them, not refugees.

OPINION: Syrian Civil War - negotiating in bad faith

Aid workers told Human Rights Watch that three camps - Ikdah, Harameen and al-Sham - near the town of Azaz were completely empty after attacks by ISIL.

The head of Ikdah camp, on the Turkish border, said ISIL had taken over the camp early on Thursday, firing shots in the air and telling residents to leave.

Doctors Without Borders (MSF) said it was "extremely worried" about the security of those displaced and access to healthcare.

The surge in violence came as representatives of Syrian President Bashar al-Assad's regime arrived in Geneva on Friday for the latest round of talks aimed at ending the war.

Syria's UN ambassador Bashar Jaafari said he had "constructive and fruitful" discussions with Special Envoy Staffan de Mistura and said his delegation proposed "amendments" to the de Mistura's blueprint for negotiations.

Jaafari's brief comments to reporters suggested the government is still focusing on the basic principles towards a political solution in Syria, and not yet willing to consider what de Mistura calls the "mother of all issues" - political transition away from President Bashar al-Assad's rule.

Outlining its bargaining position, the opposition bloc High Negotiating Committee (HNC) said it would be willing to share equally in a transitional council with the government, but repeated its rejection of a role for Assad.

Salim al-Muslet, spokesperson for the HNC, told Al Jazeera there was "no place for Assad" in the new set-up.

"I believe we're doing the right thing for our people," Muslet said from Geneva.

"The other side, the government, was forced to come here. They don't care about our people. We don't want to see any more fighting and killing. It's important that we find a solution here in Geneva.

"But there's no place for Assad or people around him who committed crimes in Syria. For us, it's important to have people who care about their own people who deserve to see an end to this nightmare."

On the ground in northern Syria, escalating fighting between Russian-backed regime forces and rebels around Aleppo city threatens a nearly seven-week ceasefire that had largely been holding.

ISIL and the al-Qaeda-linked al-Nusra Front are excluded from the truce.

The five-year conflict in Syria has killed more than 270,000 people and displaced more than 11 million people.