More than 30 people have been killed after attackers dressed as doctors stormed the largest military hospital in Kabul, Afghan officials say.

Militants armed with guns and grenades gained entry after one detonated explosives at a hospital gate and then opened fire on staff and patients.

Commandos who landed on the Sardar Daud hospital roof killed all four attackers after several hours of fighting. The so-called Islamic State (IS) group has claimed the attack. The Taliban has denied any involvement. More than 50 people were also wounded, the defence ministry said.

President Ashraf Ghani said the attack at the 400-bed hospital "trampled all human values".

"In all religions, a hospital is regarded as an immune site and attacking it is attacking the whole of Afghanistan," he said.

The attack began at 09:00 local time (04:30 GMT). One hospital staff member who was able to get out saw an attacker "wearing a white coat holding a Kalashnikov and opening fire on everyone, including the guards, patients and doctors".

One employee wrote on Facebook: "Attackers are inside the hospital. Pray for us."

The hospital attack marks a change in approach by so-called Islamic State fighters in Afghanistan - it's the first time they have engaged directly with security forces in the capital.

Previously they have targeted civilian gatherings, mainly of Shia Muslims, as well as causing carnage at the Supreme Court last month.

But at the hospital they used an approach more commonly associated with the Taliban - blowing the gates open to allow gunmen to enter. This suggests they now have the resources and the military training to expand their attacks.

If that's the case, the security forces could face more such assaults in the coming months.

In the two years since it announced its presence in Afghanistan, IS has mainly engaged with Afghan forces - and more powerful, rival Taliban fighters - in the east, near the Pakistan border. It has failed so far to widen its base in the country - one reason, observers suggest, it may now be mounting more headline-grabbing attacks.

The government claims it has rooted out IS militants from a number of bases in the east - but has yet to dislodge them from mountainous areas they control.

(Source: BBC)