Foreign Affairs Minister Charlie Flanagan says Russian actions in the Syrian city of Aleppo have had "catastrophic consequences".

Mr Flanagan was speaking following his return from the United Nations.

While there, he told the General Assembly: "The horrific human toll of the grinding conflict in Syria mounts daily and many countries in the region and far beyond are grappling with the large-scale displacement of people that this conflict has created.

Mr Flanagan has called on the Russian Federation to recognise that its military actions in Aleppo have had "catastrophic consequences for vulnerable civilians and must cease".

He said a full ceasefire observed by all sides must be restored.

"I am deeply concerned at the indiscriminate use of military force against civilians and the horrific loss of life in Aleppo over the weekend and my concerns will be conveyed directly to the Russian authorities", he said.

"This long running conflict in Syria reached new depths of barbarity in recent days and reaching a diplomatic solution is now more pressing than ever.

"I reiterate Ireland's full support of accountability for the victims of this conflict and our call for referral of the situation to the International Criminal Court.

"I have just returned from the UN which is trying, through the Secretary-General's special envoy Staffan de Mistura, to broker a diplomatic solution.

"I want to see all parties returning to the table for urgent talks that will end this horrendous conflict."

The United Nations Security Council meets to discuss Syria | Image: UN Photo/Manuel Elias

Two million people under siege

The UN Special Envoy for Syria, Staffan de Mistura, has strongly appealed to the Security Council - particularly permanent members Russia and the United States - to rescue a recently collapsed ceasefire, end the bloodshed and speed aid into the city.

Overall, some two million people remain under a de-facto siege.

"These are indeed chilling days for Syria and particularly, for the people of Aleppo, as last week was one of the worst in this six year of the conflict," Mr de Mistura told an emergency session of the council at the weekend.

Reporting that Aleppo is being reduced to rubble, Mr de Mistura reiterated his appeal for a common course of action, led by Russia and the UN, in three areas: ensuring a ceasefire; establishing weekly 48 hour pauses in the fighting to allow in aid and repairs for Aleppo's damaged water and power facilities; and allow medical evacuations for urgent cases in and around the city.

"This Council has the responsibility to relaunch the cessation of hostilities", he said.

The respective taskforces on humanitarian aid delivery and a wider ceasefire, created by the International Syria Support Group (ISSG), have been meeting separately since early this year on a way forward in the crisis.

Russia and the United States are the co-chairs of the taskforces and ISSG, which comprises the UN, the Arab League, the European Union and 16 other countries.

Mr de Mistura also said information received by Office of the UN High Commissioner for Human Rights (OHCHR) indicates dozens of airstrikes on Friday and Saturday hit residential buildings, causing scores of reported civilian deaths and injuries - including many children.

He said airstrikes are reported to have killed 213 people in Aleppo province, 139 of them in eastern Aleppo.