A suicide bomber in a minivan has attacked an army base in Afghanistan's southern Helmand Province, killing four civilians and two soldiers, officials say.

Three civilians and two soldiers were also wounded in the April 28 attack in Nad Ali district, said Omar Zwak, spokesman for the provincial governor in Helmand.

Major Abdul Qadeer Bahadorzai, a spokesman for the local army commander, confirmed the attack.

No one immediately claimed responsibility for the attack. Taliban insurgents announced the start of their annual spring offensive on April 25.

In neighboring Pakistan, gunmen shot dead four people in the northwestern tribal region along the Afghan border, a local official said.

Ikhlaq Bangash, deputy administrator in South Waziristan, said three tourists from Dera Ismail Khan and their driver were killed in the attack on their camp in the Momi Karam area on April 27 in the evening.

Bangash said the attackers burned down the camp after shooting the tourists.

No group has claimed responsibility for the killings.

Islamic militants had sanctuaries in the tribal region until a 2009 Pakistani Army offensive, after which most militants escaped to Afghanistan but some sporadically strike back.

Based on reporting by AP, dpa, Tolo News, and Dawn