The U.S.-backed and Kurdish-led militias are just two miles far from the first neighborhoods of Raqqa from the eastern side, such an advance followed a promise on Thursday that no harm would come to ISIS fighters in Raqqa who turned themselves in by the end of the month.
The Syrian Democratic Forces, which groups Kurdish and Arab fighters, has advanced to within a few kilometers (miles) of Raqqa city at the nearest point, in an offensive that got underway in November to encircle and capture the city.
The SDF, which includes the powerful Kurdish YPG militia, said earlier this month it expects to launch the final assault on Raqqa in early summer. YPG and SDF officials had previously given April start dates for the assault, but these slipped.
In a statement, the SDF said a May 15 appeal for militants to turn themselves in within 10 days had achieved "positive results", and the deadline would now be extended until May 31 based on "requests from the noble people of Raqqa".
The SDF said it would guarantee the lives of militants who turn themselves in regardless of their position, "paving the way for the settlement of their situation". The safety of their families was also guaranteed, it says.
The SDF statement issued by spokeswoman Jihane Sheikh Ahmad said the extension would "allow the greatest number possible of those who were deceived or forced to join to benefit from this opportunity".
The U.S.-led coalition says some 3,000 to 4,000 ISIS fighters are thought to be holed up in Raqqa city where they continue to erect defenses against the anticipated assault.
Between April 23 and May 23 of this year, the U.S.-led had also killed a total of 225 civilians in Syria, the Britain-based Syrian Observatory for human Rights said.
Earlier this month, the US military said that coalition air strikes in Iraq and Syria had "unintentionally" killed a total of 352 civilians since 2014.
On Wednesday, at least 16 civilians were killed in bombing raids by the US-led coalition near Raqqa, The Observatory said. The toll included a woman and her five children, as well as three couples.
"The coalition strikes hit Al-Baruda, a village about 15 kilometers (10 miles) west of Raqqa city," said Observatory head Rami Abdel Rahman.
"Most of those killed had fled eastern parts of the province of Homs," he added.
In Deir Ezzor province, A U.S.-led coalition airstrike on the town of Mayadeen early Friday killed at least 80 relatives of ISIS fighters, activists told AFP.
"The toll includes 33 children. They were families seeking refuge in the town's municipal building," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
"This is the highest toll for relatives of ISIS members in Syria," Abdel Rahman told AFP.
The latest strike came as the United Nations urged all nations bombing extremists targets in Syria to better distinguish between civilian and military targets.
U.N. human rights chief Zeid Ra'ad Al Hussein said "all states" whose air forces are active in the anti-ISIS missions needed "to take much greater care to distinguish between legitimate military targets and civilians."
The Britain-based Observatory gathered information from civilian and medical sources on the ground in ISIS-held Mayadeen, which was facing its third day of fierce bombing.
The six-year-long Syrian war has allowed ISIS to seize swathes of Syria, where the group faces separate campaigns by the U.S.-backed SDF, the Russian-backed Syrian military, and Free Syrian Army rebels backed by the United States.
More than 470,000 people have been killed and millions more displaced since Syria's conflict broke out in March 2011
