- ISIL held Manbij since 2014
- The SDF managed to encircle the city on June 10
- It was supported by US-led air strikes against ISIL
- Kurdish and Arab fighters started street fight on Thursday
Kurdish and Arab fighters of Syrian Democratic Forces (SDF) have entered a key northern city of Manbij, an ISIL stronghold, the forces and monitoring group have said.
SDF was advancing slowly to the centre of Manbij on Thursday after entering the city backed by air strikes by the US-led coalition bombing the Islamic State of Iraq and the Levant (ISIL, also known as ISIS).
Nasser Haj Mansour, an adviser to the SDF, said the forces moved into the city on Wednesday from its northern edge, close to its grain silos which are still controlled by ISIL.
"Fierce street fighting between buildings" erupted as they entered the city, said Rami Abdel Rahman, the chief of the Syrian Observatory for Human Rights.
He said progress was likely to be slow as SDF forces were facing booby-traps "planted by the jihadists to try to prevent the loss of the city".
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Abdel Rahman said tens of thousands of civilians were trapped inside the city, though some 8,000 had been able to flee since the start of the SDF offensive on Manbij on May 31.
There were fears that ISIL would use civilians as human shields inside the city, which had a population of about 120,000 before the start of Syria's civil war in 2011.
The SDF managed to encircle the city on June 10 but its advance slowed as ISIL fought back, including with almost daily suicide bombings.
A major breakthrough
The advance marked a major breakthrough in the battle for Manbij, once a key link on the supply route between the Turkish border and ISIL's de facto Syrian capital of Raqqa.
ISIL has held the city since 2014, the year ISIL seized control of large parts of Syria and neighbouring Iraq and declared its "caliphate".
Formed in October 2015, the 25,000-strong SDF is dominated by the powerful Kurdish People's Protection Units (YPG) but includes an Arab contingent that has been steadily growing to around 5,000 fighters.
As well as air support, coalition countries have provided ground advisers to the SDF, including about 200 US special forces.
The Manbij assault has coincided with another offensive launched by Syrian regime forces against ISIL in its stronghold province of Raqqa.
Backed by Russian warplanes, government forces re-entered the province this month as part of an offensive to retake Tabqa, another key town on the ISIL supply route to the Turkish border.
But after advancing to within 7km of Tabqa airbase, they were driven back late on Monday in an ISIL counter-attack that killed 40 loyalists.
Three Russian soldiers supporting regime troops in the area were seriously wounded on Tuesday when their vehicle hit a landmine, the Observatory said. They were recovered by Russian forces.
Syria's conflict began five years ago with the brutal repression of anti-government demonstrations. It has killed more than 280,000 people and displaced millions.