Thousands of civilians have fled the town of Manbij in northern Syria held by the "Islamic State of Iraq and the Levant" (ISIL) as liberating forces close in, AFP reported Tuesday (June 7th).

"We have surrounded Manbij from three sides and operations are progressing well," said Sherfan Darwish, who is leading the Syrian Democratic Forces (SDF) offensive.

"Every day, we are liberating villages," he said.

The SDF is now within five kilometres of Manbij from the north, two from the south and about seven from the east, according to the Syrian Observatory for Human Rights.

"ISIL has begun allowing civilians to flee towards the west," some in cars but many carrying their belongings on foot, said Observatory head Rami Abdel Rahman.

About 20,000 people are still living in Manbij, which had a pre-war population of about 120,000.

The coalition has carried out heavy airstrikes to support the fight for Manbij, mounting at least 35 strikes on ISIL since last week, its officers said Tuesday.

The coalition has freed a total of 344 square kilometres from ISIL since the operation to retake Manbij was launched on May 31st.

Tabqa, an ISIL-held town which lies near Syria's largest dam, is also under attack on two fronts. SDF fighters began advancing on Tabqa last week, but are still 60 kilometres away.

The Observatory said ISIL had sent a convoy of weapons and about 100 fighters to reinforce Tabqa in preparation for a major battle.