Two female suicide bombers were suspected of being behind a blast on Monday outside a stadium in northeast Nigeria, where President Goodluck Jonathan had given a speech, officials and rescue workers said.

"We have evacuated two bodies of females we believe were suicide bombers behind the blast," said one rescue worker after the explosion in Gombe city.

A bombing at a bus station in northeast Nigeria killed at least 20 people on Monday, as Boko Haram was blamed for a separate attack in the embattled region.

Violence in the northeast is escalating ahead of Nigeria's February 14 general elections, with many concerned that voting will be impossible in large parts of the region.

A convoy of suspected Boko Haram gunmen carrying grenade launchers attacked the security services, a bank and a political party office in Nigeria's restive northeast on Tuesday, witnesses said.

The attack in Gombe state came just after midday and began with a gunfight at a military checkpoint on the outskirts of Nafada town.

A triple bombing at a bus station in north Nigeria during Friday morning rush hour killed at least eight people and injured 41 others, as hopes of a ceasefire with Boko Haram appeared to suffer another blow.

It is not clear if the Islamist militants were behind the attack in Gombe city, the capital of Gombe state, but the extremists have a track record of targeting commuters.

Suspected Islamists razed a police station and killed 14 people, whose bodies were found burned, in an overnight raid in Nigeria's northeastern city of Gombe, witnesses said Saturday.

The attackers also tried to break into a prison elsewhere in Gombe in an apparent bid to free the inmates, but were unsuccessful, witnesses further said.