Syrian Kurds and allied rebels advanced against the Islamic State (ISIS) group on Tuesday, capturing a strategic town a day after seizing a base from the jihadists near their Raqa bastion.
A spokesman for the Kurdish People's Protection Units (YPG) and a Britain-based monitor said the anti-ISIS forces had taken Ain Issa on Tuesday, after capturing the nearby Brigade 93 base overnight.
"In the last few moments, Ain Issa has come under our full control, along with dozens of villages in the surrounding area," YPG spokesman Redur Khalil told AFP.
The Syrian Observatory for Human Rights, a Britain-based monitor, said ISIS forces had withdrawn from the town and YPG and rebel forces were now sweeping it to clear mines laid by the jihadists.
Ain Issa's fall comes after ISIS ceded control of the Brigade 93 base on Monday night and the border town of Tal Abyad more than a week ago.
Ain Issa and Brigade 93 are around 55 kilometers (35 miles) north of Raqa, the de facto capital of ISIS's self-declared Islamic "caliphate" in Syria and Iraq.
They both lie on a main highway that runs between Kurdish-held territory in Aleppo province to the west and Hasakeh province to the east.
The same route links territory held by the Islamic State group in Aleppo and Hasakeh provinces.
"It's also a defense line for Raqa," said Mutlu Civiroglu, a Kurdish affairs analyst. "Considering that Raqa is a sort of capital of the 'caliphate,' it creates a lot of pressure on ISIS."
ISIS "pushed back"
The YPG-rebel advance has been backed by air power from the US-led coalition fighting ISIS, with the Observatory saying at least 26 jihadists were killed in international strikes in and around Ain Issa on Monday.
"ISIS's defense lines have now been pushed back to the outskirts of Raqa city because the area between Raqa and Ain Issa is militarily weak and they have no fortifications in that area, which is mostly open plains," Observatory chief Rami Abdel Rahman said.
The advance is the latest success for YPG forces and their rebel allies, helped by US-led air strikes.
On June 16, they captured Tal Abyad on the Turkish border, which had served as a key conduit for ISIS bringing in fighters and weapons and exporting black market oil.
Kurdish forces have been chipping away at ISIS territory in the northern Raqa province for months, after successfully repelling a fierce attack by the jihadists on the border town of Kobane in January.
The YPG has emerged as "arguably the most effective fighting force against ISIS in Syria," analyst Sirwan Kajjo said after the capture of Tal Abyad.
"They are well-organized, disciplined and are big believers in their cause."
ISIS destroys mausoleums
Khalil declined to comment on where the anti-ISIS fighters would focus their attention next, but suggested an operation against Raqa was unlikely in the short-term.
"Raqa is much further away, and well-defended, it would require significant forces and weapons," he said.
Civiroglu too said any offensive against Raqa would require lengthy planning and an upgrade to the weapons available to the YPG and its allies.
"I don't see that Raqa is the next target. For now they want to consolidate their hold on Tal Abyad and the area around it," he said.
Syria's antiquities chief meanwhile confirmed ISIS had destroyed two ancient religious mausoleums in the old city of Palmyra.
Maamoun Abdulkarim said the extremists had blown up the tombs of Mohamed bin Ali and Nizar Abu Bahaaeddine, two Muslim figures.
The jihadists consider tombstones and mausoleums to be a violation of their strict interpretation of Islamic law, and have regularly destroyed both in areas they control.
AFP contributed to this report.