US-backed forces are battled on Monday ISIS militants from their former Syrian stronghold Raqqa, bringing their four-month campaign for the city to the brink of victory. Sporadic artillery fire rang out and thick columns of smoke rose above the city as US-led coalition air strikes targeted remaining jihadists in a handful of last positions. The field commander in Raqqa described Mondays fighting as "a clearing operation" and said he expected it to be completed by the end of the day with the SDF controlling the whole city. Ilham Ahmed, a senior politician in the SDF, said she expected the end of the campaign to be declared "within hours of days", but the US-led coalition said it could not put a timeline on the battle. An alliance of Kurdish and Arab fighters, the Syrian Democratic Forces, broke into Raqqa in June and is poised to seize the last 10 percent of the city after a weekend deal to evacuate civilians. "The Syrian Democratic Forces are currently waging their toughest battles yet," AFP quoted Jihan Sheikh Ahmed, spokeswoman for the operation to capture the city, as saying. The latest fighting "will bring an end to Daeshs presence," she added, using the Arabic acronym for IS. "They can choose between surrendering and dying." An estimated 300 mostly foreign ISIS fighters are surrounded, mostly in central parts of the city, but are expected to resist fiercely Overnight, SDF fighters captured the northern Al-Barid neighborhood, and their efforts would focus Monday on several adjacent districts, she added. ISIS defeat in Raqqa mirrors its collapse across Iraq and Syria, where its enemies have driven it from cities, killed its leaders in air strikes and regained the oil fields that funded its self-declared caliphate. It lost Mosul, its largest city and most prized possession after months of fighting in July. The group, which at its height ruled millions of people in both countries, is in Syria now forced back into a strip of the Euphrates valley south of Deir al-Zor and areas of desert on each side. "We have conducted some strikes in the last 24 hours, but I suspect that that will pick up here very soon with the SDF advancing into the final remaining areas of the city," said Colonel Ryan Dillon, spokesman for the US-led coalition. According to a Reuters correspondent, some cars in the streets had loudspeakers mounted on their roofs broadcasting messages to the last ISIS fighters telling them they would not be ill-treated if they surrendered. Another SDF field commander, who gave his name as Ashraf Serhad, said he had heard that 250 ISIS militants remained and that on Sunday he had seen several minivans and buses leave the hospital carrying some who had surrendered. Saturday nights convoy out of Raqqa included about 100 ISIS fighters and nearly 200 family members, said Omar Alloush, a member of the Raqqa Civil Council set up by the SDF to run the city. The fighters who left in the convoy are being held by security forces before interrogation and may be tried in court, he added.