Syrian Kurds and rebels 'advance into IS-held Raqqa province'
Syrian Kurdish fighters and rebel forces have advanced into Raqqa province, capturing 19 villages from Islamic State, a monitoring group says.
The Syrian Observatory for Human Rights said bombing raids by US-led coalition aircraft had played a key role.
Since driving IS out of Kobane last month, the Kurdish Popular Protection Units (YPG) and rebels had taken about 240 surrounding villages, it added.
They are now believed to be only 25km (15 miles) from Tal Abyad.
The strategically important border town, about 65km east of Kobane, is used by IS militants to cross into Turkey.
Fighters from the YPG and three rebel groups - Raqqa Revolutionaries Brigades, Shams al-Shamal (Sun of the North) and Jabhat al-Akrad (Kurdish Front) - have advanced steadily into IS-held territory since securing control of Kobane on 26 January.
They have reportedly captured a string of villages running eastwards along the Turkish border towards Tal Abyad, but also some further south.
On Thursday, the Syrian Observatory said there had been clashes around the cement factory owned by the French company Lafarge, north-west of Ain Issa in Raqqa province.
The YPG and its allies were also now in control of about 35km of the motorway connecting the cities of Aleppo, in the west, and Hassakeh, in the west, the UK-based group added.
Ain Issa and the motorway are 56km (35 miles) from the city of Raqqa, the de facto capital of the "caliphate" declared by IS in June after it captured large parts of Syria and Iraq.
In a separate development in Syria on Thursday, rebels captured 32 soldiers and pro-government militiamen in the village of Ratian, north of the city of Aleppo, according to the Syrian Observatory.
There has been fierce fighting in the area as the two sides try to capture territory ahead of a possible local ceasefire that UN envoy Staffan de Mistura is trying to broker.
On Tuesday, Mr de Mistura said President Assad had expressed a willingness to suspend the aerial bombardment of rebel-held areas of Aleppo for six weeks.
The UN high commissioner for human rights has meanwhile called on the Syrian government to release immediately all those who are held in its jails for peacefully expressing their views.
Zeid Ra'ad Al Hussein said that since protests against President Bashar al-Assad's rule began in March 2011, it was possible that hundreds-of-thousands of people had at some point been held in Syria's prisons.
He said detainees could be held incommunicado for weeks or months, and that this was particularly worrying given the government's record of torture and ill-treatment.