Islamic State fighters killed at least 145 civilians in an attack on the Syrian town of Kobani and a nearby village, in what a monitoring group described on Friday as the second worst massacre carried out by the hardline group in Syria.
Fighting between the Kurdish YPG militia and Islamic State fighters who infiltrated the town at the Turkish border on Thursday continued into a second day, the Syrian Observatory for Human Rights monitoring group and a Kurdish official said.
A separate Islamic State assault on government-held areas of the northeastern city of Hasaka was reported to have forced 60,000 people to flee their homes, the United Nations said, warning as many as 200,000 people may eventually try to flee.
Islamic State has a record of conducting large scale killings of civilians in territory it captures in both Iraq and Syria, where it has proclaimed a caliphate to rule over all Muslims according to an ultra-hardline vision of Islam.
The attack on the predominantly Kurdish town of Kobani and the nearby village of Brakh Bootan marked the biggest single massacre of civilians by Islamic State in Syria since it killed hundreds of members of the Sunni Sheitaat tribe last year, Rami Abdulrahman, who runs the Observatory, said.
He said 146 civilians had been killed. Kurdish officials said at least 145 had died.
The assault included at least three suicide car bombs. The dead included the elderly, women and children, he said.
The Islamic State fighters were reported to number in the dozens and entered the town in five cars disguised as members of the YPG and Syrian rebel groups.
In their other assault on Friday, Islamic State fighters clashed with Syrian government forces in the south of Hasaka for a second day and shells hit areas in the center, the Observatory said.
It appeared that Islamic State was also fanning out toward the southeast of the city, which is divided into zones run separately by the Syrian government and a Kurdish administration that oversees the YPG.
The twin attacks which began on Thursday showed the fighters returning to the offensive after two weeks of defeats at the hands of Kurdish-led forces, supported by U.S.-led air strikes. Earlier this week the Kurds advanced to within 50 km (30 miles) of Raqqa city, the de facto capital of Islamic State's self-declared caliphate.
In the latest battles, Islamic State has picked targets where it is difficult for the U.S.-led alliance to provide air support to those fighting on the ground. In Kobani, also known as Ayn al-Arab, aerial bombardment risks civilian casualties in residential areas targeted in the attack.
In Hasaka the Islamic State targets were in areas controlled by President Bashar al-Assad. The U.S.-led coalition, which has been bombing Islamic State targets in both Syria and Iraq since last year, has ruled out cooperating with Damascus.
Huge displacement in Hasaka
Kobani was the site of one of the biggest battles against Islamic State last year. The Kurdish forces eventually drove the militants out of the town in January with the help of U.S. air strikes and Iraqi Kurdish fighters, after months of battles.
Recent weeks have seen momentum shift repeatedly in the battle against Islamic State. The fighters advanced rapidly last month, seizing cities in Syria and Iraq, before the recent Kurdish advances in Syria. Islamic State fighters have often adopted a tactic of attacking elsewhere when they lose ground.
The group wrested control of at least one district of Hasaka city in its raid there on Thursday. The U.N. Office for the Coordination of Humanitarian Affairs said an estimated 50,000 people had been displaced within Hasaka city while 10,000 had left northwards toward Amuda town, close to the Turkish border.
Speaking to Syrian state TV, the governor of Hasaka said the city was "safe and secure" and urged people to return home.
The Observatory said fighting was continuing. Government forces were carrying out air strikes targeting areas south of Hasaka controlled by Islamic State, it added.
State news agency SANA said scores of Islamic State fighters were killed in the bombardments. This could not be independently confirmed.
Assad has lost territory since March in areas of northwestern, southern and central Syria to a patchwork of armed groups, including Islamic State, other hardline Sunni jihadists, and rebels who profess a more inclusive vision for Syria.
The Observatory said at least 34 people had been killed in Deraa province in southern Syria since an insurgent alliance known as the Southern Front launched an operation on Thursday to capture the remaining areas of government control. Those killed included rebel fighters and a media activist, it said.
The head of one of the rebel groups fighting in the south said there had been progress, but it was not fast.
"The battle continues," Bashar al-Zoubi, the head of Yarmouk Army, told Reuters.
Al Qaeda's Syria wing Nusra Front also has a presence in the south. SANA said the army had targeted Nusra Front on Friday, killing a number of fighters and destroying their weapons.
The government has focused on shoring up control over the main cities in the west, including Damascus, with vital military support from the Iranian-backed Lebanese group, Hezbollah.