Gunmen killed 15 soldiers and wounded more than a dozen others during an attack on an army base in Kaduna state, two army sources said on Tuesday, in the latest attack on security forces by armed gangs.

The gangs, designated as terrorists by the government, have caused havoc in northwest Nigeria by attacking villages, towns and schools and kidnapping hundreds of students.

An army officer at the military base in the town of Birnin Gwari in Kaduna told our correspondent that gunmen on motorbikes used rocket-propelled grenades and other heavy weapons during an attack that lasted more than two hours on Monday evening.

Eleven soldiers died during the attack while 19 were injured and taken to three different hospitals in Kaduna. Four soldiers later succumbed to their injuries, the officer said.

"These are not ordinary bandits I know that we are fighting. The bandits took away several weapons from our base," said the officer, who declined to be named because he is not authorised to speak to the media.

An army spokesman did not respond to several calls and messages on his mobile phone on Tuesday.

Birnin Gwari shares a border with Zamfara and Niger states, which are among the hot spots of armed gangs.

Another soldier at the Kaduna base said three military vehicles were destroyed during the attack and several guns were missing from the armoury.

A situation report from the base to the army headquarters in Abuja seen by Reuters said the situation "is calm but highly unpredictable."

Nigeria's military is stretched as it fights an Islamist insurgency in the northeastern part of the country and the armed gangs in the northwest.

Reuters