BEIRUT -- In another setback to international efforts to resolve Syria's devastating civil war, peace talks are not to resume next week in Geneva, a UN envoy announced as Turkey on Friday intensified cross-border artillery shelling on areas dominated by Syria's U.S.-backed, mostly Kurdish militia.

But reinforcing its image as a key force battling the Islamic State group on the ground, the predominantly Kurdish coalition, known as the Syria Democratic Forces, on Friday captured the town of Shaddadeh in the country's northeast. The town was one of the biggest strongholds of the extremists.

Meanwhile, Russia called for an urgent Security Council meeting over the deteriorating border situation. A statement posted on the Russian foreign ministry's website said it intends to submit a draft council resolution calling on Turkey to "cease any actions that undermine Syria's sovereignty and territorial integrity."

In comments to Swedish newspaper Svenska Dagbladet, UN Special Envoy for Syria Staffan de Mistura, said the Syria talks won't resume in Geneva on Feb. 25 as he had previously hoped. He said that he cannot "realistically" get the parties in the Syrian conflict back to the table by then, "but we intend to do so soon."

Fighting has fighting intensified in Syria over the past weeks and a deadline to cease military activities has not been observed. The United States, Russia and other world powers agreed Feb. 12 on a deal calling for the ceasing of hostilities within a week, the delivery of urgently needed aid to besieged areas of Syria and a return to peace talks in Geneva.

De Mistura halted the latest Syria talks on Feb. 3, because of major differences between the two sides, exacerbated by increased aerial bombings and a wide military offensive by Syrian troops and their allies under the cover of Russian airstrikes.

In an interview published late Thursday on the Swedish daily's website, de Mistura said, "We need real talks about peace, not just talks about talks."

In recent weeks, Syrian government forces captured dozens of villages and towns across the country while the SDF evicted opposition fighters and militants from areas near the border with Turkey in Aleppo province.

Ankara strongly opposes the SDF, which is composed mostly of Kurdish fighters and has become one of the most effective forces on the ground fighting the Islamic State group.

The International Committee of the Red Cross expressed deep alarm, over the situation Aleppo, saying the intensified fighting there has forced 70,000 people to flee their homes and left many without water or electricity.

ICRC said in a statement Friday that two hospitals hit earlier this week in Aleppo left them out of service. The clinics had provided thousands of consultations, surgeries and delivered hundreds of babies per month. The Red Cross also said the remaining hospitals that work in the area are struggling to function.

In yet another blow, international rights group Amnesty International said Turkish authorities have denied entry to wounded Syrian civilians in need of immediate medical care after they fled the intense bombardment of the Aleppo countryside over the past two weeks.

Amnesty said it has also documented how Turkish security forces have shot and wounded civilians, including children, who out of desperation have attempted to cross the border unofficially with the help of smugglers.

"People we spoke to painted a tragic picture of the desperate situation for the civilians who remain trapped between daily airstrikes and dire humanitarian conditions," said Tirana Hassan, Crisis Response Director at Amnesty International. "Turkey's highly selective practice is appalling - only severely injured people are allowed entry to seek medical treatment while everyone else fleeing the violence is left unprotected."

Amnesty said the border must remain open to all those fleeing conflict in Syria especially the injured and sick civilians being targeted by daily airstrikes on their homes, hospitals, and schools.

Earlier Friday, a rebel commander in the northwestern province of Idlib said Turkey was facilitating the movement of other rebel factions specifically in order to weaken the SDF. The commander, who spoke on condition of anonymity because he was not authorized to reveal military secrets, said a mixed coalition of rebel fighters were permitted to pass into Turkey and enter Syria again in order to prevent the city of Azaz from falling into SDF hands.

Azaz is currently held by Turkish-backed rebel factions and is surrounded by both SDF forces and Islamic State group fighters.

SDF gains in the area south of Azaz triggered several days of Turkish shelling, mainly targeting areas recently captured by the group. On Thursday night, Turkish troops intensified the shelling with ongoing barrages that lasted until early Friday.

An SDF official said Turkish troops were bombing their positions in border areas, inflicting casualties among civilians. Ahmad al-Omar said the shelling hit several areas, including the town of Jandairis on Friday.

The Britain-based Syrian Observatory for Human Rights said the shelling on areas on northern Syria lasted seven hours, killing two and wounding several people.

The SDF is dominated by the main Kurdish militia known as YPG. Turkey blames both the YPG and its own domestic Kurdish rebels for Wednesday's bomb attack in Ankara that killed 28 people. Late Friday, the Turkey-based Kurdistan Freedom Falcons -- an offshoot of the Kurdistan Workers' Party, or PKK -- claimed responsibility for the Ankara attack.

In Syria, the taking of Shaddadeh in the northeastern province of Hassakeh from the IS hands a two-day SDF offensive in the area, according to the Observatory and SDF spokesman Talal Sillo.

The town's capture is a blow to the Islamic State and would further boost the SDF, which sees the extremist IS group as its primary enemy on the battlefield in Syria's complex and multi-layered civil war.

Sillo said SDF cut all supply lines to Shaddadeh, which was surrounded from all sides, before storming it. He said the mostly Kurdish forces lost six fighters and claimed that dozens of bodies of killed IS fighters were strewn on the ground in villages and roads near the town.

"We have fully liberated Shaddadeh" Sillo said by telephone from northern Syria.

Associated Press writer Suzan Fraser contributed to this report from Ankara, Turkey