Theresa May makes plea to European leaders for Syria resolution

British prime minister Theresa May has appealed to other European leaders to put further pressure on Russia in an attempt to cease hostilities in Syria.

The northern city of Aleppo has been under siege for weeks after a ceasefire broke down between the warring factions, and tensions remain high despite a brief respite on Thursday.

In a speech delivered in Brussels, May called on the other leaders to maintain a strong and united front, and promised that Britain would be a dependable partner despite its looming departure from the bloc.

"It is vital that we work together to continue to put pressure on Russia to stop these appalling atrocities, these sickening atrocities, in Syria," she said.

May's appearance at the European council meeting will be the first time she has faced all other European leaders since the UK's vote to leave Europe in June.

"The UK is leaving the EU, but we will continue to play a full role until we leave and we'll be a strong and dependable partner after we've left," May said.

European council president welcomed May to the meeting, dispelling fears that she would be treated badly.

"Some media described her first meeting in the European council as entering the lion’s den," he said. "It's not true. It's more like a nest of doves. She'll be absolutely safe with us."