Turkey is negotiating with Russia to open a corridor to evacuate Syrian rebel fighters and civilians from the remaining opposition-held districts of Aleppo, but no agreement has yet been reached, a senior Turkish official said.

Rebel defences in Aleppo collapsed on Monday, leading to a broad advance by the Syrian army across more than half of the remaining insurgent pocket in the city and a retreat of opposition fighters to a few districts.

“Efforts are still underway to open a corridor for the rebels and civilians in Aleppo, and evacuate them from the region. There has been no agreement on this issue yet,” the Turkish official told Reuters, speaking on condition of anonymity.

“Turkish and Russian officials are expected to meet in Turkey tomorrow and evaluate the situation. The meeting will put the issue of opening a corridor, as well as a ceasefire, on the table,” the official said.

Turkish Foreign Minister Mevlut Cavusoglu said a ceasefire was needed to allow civilians to be evacuated and Ankara would intensify talks in coming days with Russia and other countries, although he said they were already in constant contact.

“We’re seeing the most cruel form of savagery in Aleppo, and the regime and its supporters are responsible for this. The wounded are not being let out and people are dying of starvation,” he told a news conference in Ankara.

“However, we will continue our efforts. Even if everyone remains silent, we will not be silenced...We always come up with concrete proposals, but we saw that many countries were not sincere,” Cavusoglu said.

A fighter with an opposition group inside Aleppo confirmed that there were talks between Russia and Turkey but had little hope they would succeed.

“They are talking and they are failing because Russia is not really offering anything,” he said from inside Syria by phone.

An official from the rebel Turkmen Sultan Murad brigade said there was little incentive for them to accept anything that had been discussed so far.

“They keep coming back with the same unacceptable demands and present it as an offer. These are not real offers,” said the official, based in the southern Turkish city of Gaziantep.

Rebel factions did not want to leave Aleppo, he said.