ADDIS ABABA (Reuters) - An explosion on a bus in northern Ethiopia killed eight people and wounded 27 on Thursday, a police official said, blaming the attack on agents from Ethiopia's arch-foe Eritrea.

A federal police commander, Demash Hailu, said the bus had been travelling between the towns of Humera and Shire in the north's Tigray region.

"Investigations have shown that the bomb was planted by Eritrean agents," Demash told Reuters, without giving further details.

Ethiopia has often accused Eritrea of being behind blasts on its territory.

Demash also said "many" young Eritreans, including soldiers had crossed into Ethiopia in recent days -- without giving more information.

The two Horn of Africa neighbours, which fought each other in a two-year war ending in 2000, are locked in a bitter impasse over their 1,000 km (620 mile) border.