At least 26 Afghan soldiers have been killed and 13 wounded in a Taliban attack on a military base in Kandahar province, according to the defence ministry, in the latest blow to struggling security forces.

The attack happened late on Tuesday in the Karzali area of Khakrez district.

At least 21 other people went missing and seven were kidnapped, General Dawlat Waziri, Afghan defence ministry spokesman, told Al Jazeera.

"Afghan soldiers resisted the attack and the fight is now over, they [Taliban fighters] were unable to take over the base," he said.

He said more than 80 fighters were killed in the counterattack.

However, the Taliban claimed to have killed at least 70 soldiers and to have seized a number of army vehicles, equipment, machinery and weapons.

Al Jazeera's Jennifer Glasse, reporting from Kabul on Wednesday, said the attack in Khakrez lasted four hours.

"This is just the latest assault in a concerted offensive by the Taliban all over the country," she said.

"Earlier this week they attacked in Faryab province in the north, in Ghor and Badghis in central Afghanistan, and today [on Wednesday] they launched another offensive in the east in Nuristan province."

"It seems like a concerted strategy by the Taliban to try and keep Afghan security forces stretched thin and on their back foot."

The Taliban has carried out increasingly complex attacks against security forces so far in 2017.

In April, more than 140 soldiers were believed to have been killed on a base outside the northern city of Mazar-i-Sharif, one of the deadliest ever Taliban attacks on a military installation.

Taliban advances

A month earlier, armed men disguised as doctors stormed Kabul's Sardar Daud Khan hospital - the country's largest military hospital - and killed dozens.

According to US watchdog SIGAR, casualties among Afghan security forces soared by 35 percent in 2016, with 6,800 soldiers and police killed.

Over the weekend, the Taliban overran two district centres - Taywara and Kohistan - in northern and central Afghanistan.

There has been a surge in fighting in several northern and southern Afghan provinces in recent days, including in Helmand in the south.

There, amid the fighting, a US air raid on Friday killed at least 16 Afghan police officers in friendly fire.

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Afghan troops and police are battling largely alone on the ground against anti-government forces, after US-led foreign forces withdrew from most combat operations in December 2014.

The US is actively considering sending more troops to Afghanistan and US commanders there have requested thousands of extra soldiers on the ground.

The US contingent now numbers about 8,400, and there are another 5,000 from NATO allies, a far cry from the US presence of more than 100,000 six years ago. They mainly serve as trainers and advisers.