Syrian government forces have launched a new operation targeting underground tunnels used by the Islamic State group in the capital Damascus, according to state TV.
The aim of the operation is to destroy trenches and tunnels in the Hajar al-Aswad neighbourhood and the nearby Palestinian refugee camp of Yarmouk that is also mostly controlled by IS, it was reported.
A group of journalists taken to the adjacent neighbourhood of Qadam witnessed intense shelling and air strikes on IS positions in the camp and Hajar al-Aswad.
The area in southern Damascus is the last part of the capital not controlled by President Bashar Assad's forces.
Other insurgents in the area, including an al Qaida-linked group, have said they would relocate to rebel-held regions in northern Syria.
Meanwhile, UN Syria envoy Staffan De Mistura warned that the northern rebel-held province of Idlib could become the conflict-ravaged country's newest humanitarian crisis area.
His warning came as international donors gathered in Brussels to drum up emergency support.
Mr De Mistura said that "Idlib is the big new challenge - 2.5 million people".
He told reporters that "there are women, children, civilians, and this is looming up there".
Mr De Mistura hopes the two-day donor conference "will be an occasion for also making sure that Idlib doesn't become the new Aleppo, the new eastern Ghouta, because the dimensions are completely different".
The Syrian Observatory for Human Rights says 177,000 people have fled combat in eastern Ghouta since February. The rest - including about 12,000 fighters - relocated to Idlib.