Nigerian Boko Haram Islamists launched an attack Monday on a military base in northwest Cameroon, forcing many to flee the area, the official sources said.

"As soon as people heard the first gunfire they fled the city" of Kolofata, a local Cameroonian source told AFP.

A Nigerian archbishop called Monday for the same international support to tackle Boko Haram as France has received since it was hit by Islamist attacks last week.

"I see the very positive response of the French government tackling this issue of religious violence after the killing of their citizens," said the Roman Catholic Archbishop of Jos in central Nigeria, Ignatius Kaigama.

Four people were killed in the northeast Nigerian city of Potiskum on Sunday, when two female suicide bombers, one of them aged about 15, blew themselves up in a crowded market.

The blasts at the Kasuwar Jagwal mobile phone market in the commercial capital of Yobe State came just a day after a young girl thought to be aged only 10 killed 19 in Maiduguri, in neighboring Borno State.

Nigeria's military has called for support in tackling Boko Haram after a major attack on a key northeast town that is feared could be the worst in the bloody six-year insurgency.

There are still no independently corroborated figures for the huge numbers said to have been killed in Baga, on the shores of Lake Chad in the far north of Borno State.

At least two people were killed when a car exploded at a police station in Potiskum, northeast Nigeria, an officer told AFP.

The blast at the facility attached to the Potiskum Area Command at about 3:30 pm (1430 GMT) involved a driver and vehicle which had earlier raised suspicions at a checkpoint outside the city.

The United States condemned a spike in attacks in northeastern Nigeria by Boko Haram, urging all responsible for the "recurring terrorist attacks" to be held accountable.

The wave of unrest -- starting last week when Boko Haram invaded the fishing town of Baga in northern Borno State, believed to be the worst attack in the bloody six-year insurgency -- has left homes burnt to the ground and caused at least 20,000 people to flee.

At least 19 people were killed on Saturday when a young girl, thought to be aged about 10, blew herself up at a crowded market in the restive northeast Nigerian city of Maiduguri.

The powerful explosion rocked the city's Monday Market at about 12:40 pm (1140 GMT) when it was packed with shoppers and traders. The same market was hit twice by female suicide bombers late last year.

A spike in Boko Haram attacks in northeastern Nigeria has sent some 7,300 people fleeing to neighbouring Chad in a matter of days, the U.N. refugee agency said on Friday.

Members of the armed Islamist movement on Saturday captured the town of Baga in Borno state.

Boko Haram razed at least 16 towns and villages in a renewed assault after capturing a key military base in restive northeast Nigeria at the weekend, local officials said on Thursday.

Heavy casualties were feared in the attacks on Wednesday in the remote north of Borno state, according to local sources, but there was no independent corroboration of the figures cited.

Boko Haram leader Abubakar Shekau has threatened Cameroon in a video message on YouTube, warning that the same fate would befall the country as neighboring Nigeria.

The video, which was posted on January 5, is directly addressed to Cameroon's President Paul Biya after repeated fighting between militants and troops in the country's far north.