Afghan government forces in the last two months have suffered heavy casualties across the country, threatening a fragile peace deal between the United States and the Taliban.
The Taliban on Monday claimed responsibility for a truck bomb in southern Helmand province that killed at least five Afghan security force members, an Afghan official said, adding to weeks of rising violence in the country.
Sunday evening's attack took place at a military centre where at least 150 members of the Afghan army and intelligence wing were stationed, according to government officials and the Taliban.
"Five Afghan security forces members were martyred and seven others wounded in a truck bomb blast in Grishk district," a spokesman for Helmand's provincial governor, Omar Zwak, said.
The Afghan Defence Ministry had earlier confirmed the blast but said only one member of the army was injured.
An intelligence officer who survived the attack at the military centre told Reuters that militants detonated a truck bomb near the facility for members of the National Directorate of Security (NDS) and the army.
Speaking on condition of anonymity because of the sensitivity of the matter, the official said he helped pull out at least 18 bodies from the blast site on Sunday night.
The Taliban said the toll was much higher.
"Dozens of members belonging to the enemy forces have been killed and wounded in the attack," Qari Yousuf Ahmedi, a spokesman for the militant group, said in a statement.
A guard at the centre said he had shot and killed the driver of a truck that had driven up close to the premises.
"When other security forces came out, suddenly a huge explosion happened and I lost consciousness,” the guard, Sher Ali, said. He added that he did not know how many were dead but at least eight fellow guards were with him when the explosion happened.
Afghan government forces in the last two months have suffered heavy casualties across the country. The violence poses an immediate threat to a fragile peace deal between the United States and the Taliban, signed in February, as the military is forced to fight an emboldened Taliban with less US support.
In a separate incident, police in southeastern Paktika province said at least 20 people were injured when Taliban fighters threw a hand grenade into a mosque in Khayerkot district on Sunday evening.
The United States recorded an increase in Taliban attacks against Afghan forces in March after signing the peace deal, a government watchdog office said last week, contrary to hopes that the deal would lead to a reduction in violence.