MAZAR-I-SHARIF, Afghanistan (Reuters) - Samad always worried that something might happen to his brother, Shah Mohammad, a three-year veteran of the Afghan army, even though his job was to train soldiers, not to fight.

Bullet holes are seen on the wall of a mosque at the military headquarters where the Taliban attack occurred last week in Mazar-i-Sharif, northern Afghanistan April 25, 2017. REUTERS/Stringer

“He used to tell us that since he doesn’t go to the battlefield, he was fine inside the base,” Samad said.

On Friday, the base in northern Afghanistan became a death trap for Mohammad and scores more, when suspected Taliban fighters killed more than 140 soldiers in what is believed to be the deadliest attack on Afghan forces since the fall of the Taliban in 2001.

Photographs and video footage from the dining hall where Mohammad died, as well as the nearby mosque, reveal the fury of the attack at the base in the city of Mazar-i-Sharif.

Buildings are pockmarked with hundreds of bullet holes and windows have been shattered, while charred copies of the Koran lay scattered on the floor. Five days after the attack, blood still stains some walls.

Shah Mohammad’s body was so badly burned that Samad, who traveled from the brothers’ home in Takhar province, at first had trouble identifying him.

As of Tuesday, more than 40 similarly burned bodies remained unidentified, officials said.

The security failure and scale of casualties has led to questions over the government’s ability to stabilize the country, and prompted the resignation of the Afghan defense minister and army chief of staff on Monday.

General Momand Katawazi, commander of the 209th Corps which is headquartered at the base, has been reassigned to Kabul.

Only last month, gunmen dressed as medics infiltrated Afghanistan’s largest military hospital and killed dozens of patients, guards and medical staff in Kabul.

Officials are investigating exactly how the Mazar-i-Sharif attackers gained access to the base, after witnesses said they talked their way past the first checkpoint and cleared several others, including a set of metal doors that can only be opened from inside.

DEAD AND WOUNDED

There is still no official death toll, although several officials have put it at around 140.

Privately, some officials say the number killed is likely to be significantly higher, but fear that releasing the real figure could sap the morale of Western-backed security forces already struggling to battle a resurgent Taliban and other militant groups.

What is known is that at least 10 militants in fatigues drove up to the base’s gates on Friday in two trucks, waving identification cards and claiming to have a wounded soldier in need of urgent medical care.

One truck was mounted with a machine gun, which the attackers used to gun down worshippers at the mosque, many of whom were new recruits attending Friday prayers.

At the base’s dining hall, witnesses said one attacker set down his weapon and pretended to guide soldiers to safety, only to lock the door behind him and set off a suicide vest in their midst.

As Afghan commandos arrived, remaining militants took up position in a small room in the mosque, where they resisted for five hours before being killed.

American military advisers were present elsewhere on the base during the attack, but were not actively involved in responding, U.S. officials said.

INSIDER ATTACK?

At least four soldiers are suspected of having helped the Taliban, but officials say they remain at large. Two others are in custody, an official said, but did not describe what they were suspected of.

The Mazar-i-Sharif attack was probably made worse by one of the measures brought in to prevent such bloodshed.

Some military bases in Afghanistan have limited the number of troops carrying weapons, in order to guard against insider attacks by militant sympathizers or disgruntled recruits.

Between January and November, 2016, more than 150 Afghan soldiers and police died at the hands of fellow security forces, according to the Special Inspector General for Afghanistan Reconstruction, a U.S. government watchdog.

“Our soldiers inside the base do not carry weapons with them and there are only armed guards outside key buildings and checkpoints,” said Nasratullah Jamshidi, an army spokesman.

As the attack unfolded, officers radioed security guards, ordering them not to return fire as they thought it was a misunderstanding or dispute between soldiers, said Ahmad Saboor, a guard at the base.