Afghan forces are suffering higher combat casualties this year, with up to 9,000 troops killed or wounded in battles with Taliban insurgents, the new US commander in Afghanistan said Thursday.

The casualties have sky-rocketed over the past two years as NATO's US-led force has scaled back its presence and handed over most combat duties to the Afghan policy and army.

General John Campbell, who recently took over as head of the NATO-led International Security Assistance Force in Afghanistan, told reporters the estimate "for overall (Afghan) casualties -- this includes both wounded and killed -- is in the neighborhood of 7,000 to 9,000 for '14."

And for the whole of 2013, the total number of casualties for Afghan security forces was "about the same number," the general said via video link from Kabul.

"There has been an uptick in the number of casualties that the Afghan security forces have taken. But that was expected because they're in the lead," after taking over from the NATO mission, he said.

Afghan police were particularly hard hit because they had less equipment and were more vulnerable, said Campbell, who assumed his post six weeks ago.

"There's a much greater percentage rate on the police because that's really the first line of defense," he said. "They're not equipped at the same level that the Afghan army and the special operating forces are equipped. So they've probably taken the brunt of those casualties."

Fierce fighting in recent weeks in the southern Helmand province, where a large contingent of US Marines has withdrawn, had pushed the casualty numbers higher, the general said.

"Helmand ... for the last six weeks has been a pretty good fight," he said.

But he predicted Afghan troops would succeed in pushing back the Taliban, saying the insurgents were unable to "hold" territory.

He said "in the next 48 hours you'll see reports from the Afghans that show that they've done very, very well there."

More than 2,200 US troops have been killed in 13 years of war in Afghanistan and more than 19,000 wounded. But the casualties have dropped dramatically since American and NATO forces began drawing down over the past two years, while playing a supporting role to Afghan troops.

Apart from US special operations forces, most American soldiers no longer take part in combat operations in Afghanistan. There are nearly 40,000 American troops still in the country and that number is due to drop to 9,800 by the end of the year under a US-Afghan security agreement signed this week.

After the September 11, 2001 attacks by Al-Qaeda on New York and Washington, the United States invaded Afghanistan, toppling the Taliban regime for its ties with Al-Qaeda extremists.