The first blast late Thursday destroyed the office which was based inside a mosque in Khost city, they said, adding that the casualties occurred when another went off nine minutes later as police reached the area.

“A bomb explosion destroyed the election registration office in Khost city last night. When police secured the area a secondary explosion wounded two police,” provincial deputy police chief Mohammed Zaman told AFP.

The electoral office has been set up inside a large mosque located near the provincial police headquarters, residents said.

A similar attempt was foiled a week ago when police defused a bomb in the same office, Zaman added.

Abdul Rehman Mohibat, the director of the UN-backed joint electoral management board, also confirmed the attack.

Suspected militants from the ousted Taleban regime have stepped up attacks in the south and east of the war-torn country in recent months. More than 600 people have died in political violence since the beginning of this year.