Beirut: Kurdish fighters battled the Islamic State group in northern Syria on Tuesday after President Barack Obama said the US-led coalition was intensifying its campaign against the jihadists in the conflict-riven country.
The extremist group launched a major offensive on Monday against villages controlled by the Kurds in the northern provinces of Raqa and Hasakeh, prompting fierce clashes.
The Syrian Observatory for Human Rights, a British-based monitor, said about 80 IS fighters had been killed since Sunday morning in fighting and intensified US-led air strikes that began over the weekend.
Obama said the US-led coalition battling the jihadist group -- also known as ISIL -- would step up its campaign in Syria, while cautioning that a long battle remained.
"We`re intensifying our efforts against ISIL`s base in Syria. Our air strikes will continue to target the oil and gas facilities that fund so much of their operations," he said.
Obama said the group`s "strategic weaknesses are real," noting it has no air force and no support from any nation.
But he cautioned that the fight would likely face "setbacks" and would not be quick.
"This is a long-term campaign," he said.
"In many places in Syria and Iraq, it`s dug in among an innocent civilian population. It will take time to root them out."
He said more than 5,000 air strikes had been carried out against the group, eliminating "thousands of fighters, including senior ISIL commanders."
In recent days, the US-led coalition has launched a series of heavy air strikes against IS, particularly targeting its de facto Syrian capital of Raqa city.
On Saturday night and Sunday morning, nearly 30 IS fighters were reported killed in US-led raids in and around the city, with infrastructure including bridges also destroyed in the strikes.
According to US Defence Secretary Ashton Carter, the recent strikes were not targeting particular IS figures, but were intended to help Kurdish forces.Since the US-led raids in Syria began last September, they have been key to helping Kurdish forces repel IS and take territory from them.
In January, Kurdish forces secured the symbolic border town of Kobane after four months of IS attempts to overrun it.
And in recent weeks, they seized the key town of Tal Abyad from IS, depriving the group of a conduit through which it transported weapons and fighters.
But IS has fought back, launching a major offensive against Kurdish forces on Monday in parts of northern Raqa province and northwestern Hasakeh province.
The Observatory reported that the jihadists took the town of Ain Issa, around 55 kilometres (34 miles) from Raqa, during the offensive, but Kurdish officials and activists said an attack by the jihadists had been repelled.
"There are still some pockets in the south of the town," Kurdish activist Mustafa Ebdi told AFP, adding that the anti-IS forces were being backed by US-led strikes.
"There are dozens of jihadist bodies on the battlefield," he said.
The Kurds successfully regained control elsewhere of more than 10 villages in Raqa and Hasakeh that were briefly overrun during the IS offensive, the Observatory said.
"The coalition aircraft have played an effective role in the recapture," Observatory chief Rami Abdel Rahman said.
Heavy fighting was continuing on Tuesday in several areas in the two provinces where IS was on the offensive, he added.
Elsewhere, at least 25 regime troops were killed when a suicide bomber from Al-Qaeda`s Syrian affiliate Al-Nusra Front struck an army base in western Aleppo on Monday, the Observatory reported.
The attacker blew himself up inside a vehicle "in front of an orphanage used by the regime as a base in al-Zahra neighbourhood."
Two rebel coalitions last week launched attacks against government-held areas in western Aleppo, and heavy fighting continued Tuesday in the Zahra neighbourhood, the Observatory said.
Once Syria`s economic powerhouse, Aleppo has been divided between government control in the west and rebel control in the east since shortly after fighting arrived there in mid-2012.