NEW DELHI, Oct. 24—Indian officials reported today that unprovoked Pakistani mortar shelling of Indian border towns had killed at least five civilians and wounded 25. The towns were in the states of Assam and Tripura, on East Pakistan's eastern border.

According to an Indian news agency, the officials said that the mortar shells fell during the day on the towns of Agartala and Kamalapur in Tripura and on several villages in the Karimganj area of Assam.

The shelling was said to have caused panic for a few hours in Agartala, and electric power was knocked out there for some time.

Border clashes between Indian and Pakistani troops have become frequent, particularly on the eastern frontier. The Indians have been providing the Bengali insurgents with border sanctuary and some arms and training. Border clashes occur when the Bengali insurgents are heading back to their Indian sanctuaries after a guerrilla raid, and the Pakistanis are in pursuit.