A bomb, planted inside a minibus carrying the workers to voter registration sites in eastern Nangarhar province, exploded before 8:00 am (0330 Saturday), UN spokesman Manoel de Almeida e Silva told AFP.

"The information we have now is that three of them were killed and that three or four are seriously wounded," he said.

"They were all Afghan, they were all women."

Local officials confirmed the attack and said three people had died.

"Among the three killed, one of them is the child of one of the women killed," deputy security director of Jalalabad city Abdul Rehman said.

The vehicle has been destroyed, he added.

A minibus rented by the electoral secretariat exploded Saturday morning killing at least two people, deputy governor Asif Qazizada said.

The vehicle had left its office in eastern Jalalabad city and was on its way to Shinwar district when the blast occurred.

"As soon as they are two kilometres out of Jalalabad city, the bomb -- already placed inside the car itself -- explodes killing two women working for the electoral commission and injures another 11," provincial commander Hazrat-i-Ali said.

The driver, who was not injured, has been arrested and is facing interrogation, he said.

Voter registration has been going on in preparation for September's first presidential and parliamentary elections since December 2003.