US-backed fighters inched forwards in Raqqa's Old City against fierce resistance Wednesday, after penetrating the heart of the Daesh's (ISIS) Syrian bastion, a spokesman and a monitor said.
The Syrian Democratic Forces -- an alliance of Kurdish and Arab fighters -- entered the historical quarter after air strikes by the US-led coalition punched two holes in its ramparts late on Monday.
The extremists deployed four weaponized drones and several suicide bombers in vehicles against the advancing fighters, said a spokesman for the Kurdish People's Protection Units (YPG), which makes up a bulk of the SDF.
"The SDF advanced and captured the strategic Saif al-Dawlah road leading towards the Old Mosque," Nuri Al-Mahmoud told .
The Syrian Observatory for Human Rights said the SDF had pushed forwards about 200 metres (yards) by midday (0900 GMT) on Wednesday.
"They are now approximately 300 metres (yards) from the Old Mosque -- within firing range of it," said Observatory head Rami Abdel Rahman.
The US envoy to the coalition, Brett McGurk, hailed the SDF's entry into the Old City as a "key milestone" in the campaign to defeat IS in its de-facto Syrian capital.
Raqqa earned notoriety as the scene of some of the group's worst atrocities, including public beheadings, and is thought to have been a hub for planning attacks overseas.
Tens of thousands of civilians are believed to be trapped inside the city, with warnings that the extremists are using them as human shields.
Many who have managed to escape say Daesh snipers are targeting those trying to flee.
The coalition estimates that around 2,500 besieged extremists are defending Raqqa
