Angus Robertson has urged Theresa May to do everything she can to bring an end to hostilities in the Syrian city of Aleppo as he warned "time is absolutely of the essence".
The SNP's leader in Westminster told the Prime Minister that the situation in the besieged city was now so bad that "it could be one of the biggest massacres of a civilian population since World War Two" as he pressed for immediate action.
The Prime Minister said the Government was "pressing hard" and "doing everything that we can" to end the suffering of the Syrian people.
Mrs May said: "You are right to draw attention to the appalling situation that is taking place in Syria and particularly the indiscriminate attacks that we see on civilians in Aleppo.
"The United Kingdom has been working with France to bring forward an emergency discussion on this issue at the UN Security Council that will take place later today.
"We want to see a cessation of hostilities. We want to see an opportunity for aid, humanitarian aid to have access to Aleppo and we will be pressing for that at the Security Council."
Mr Robertson welcomed the UN discussions but stressed the need for immediate action as the situation in Aleppo continues to deteriorate.
"Time is absolutely of the essence," he said during Prime Minister's Questions.
"I know the Prime Minister is seized of this matter, we are in agreement.
"Please can I appeal to you, can absolutely everything be done now to alleviate the situation of the poor people of Aleppo and of Syria?"
Mrs May replied: "You are right about the horrific situation that exists in Aleppo.
"I can assure you that the Government is pressing hard, is doing everything that we can in relation to this.
"We have consistently looked at what might be the possible solutions to see if there are other avenues that we can press for.
"I think the Security Council debate is very important and there is an important message to send to Russia that they actually use their influence with the Assad regime to stop these appalling atrocities in Aleppo and let humanitarian aid through."