Abuja - Nigerian warplanes are carrying out air strikes against Boko Haram militant bases in northeast Borno state, a senior official said on Friday, in a government counter-attack against the group's apparent drive to create an Islamist enclave.
The official, who asked not to be named, told Reuters Nigeria's military was battling Boko Haram fighters at Bama, 70 km (45 miles) southeast of the Borno state capital Maiduguri.
Air strikes have been carried out "on all the Boko Haram bases", the official said, adding this reflected President Goodluck Jonathan's order for a "fully-fledged war" against the group which has waged a bloody insurgency since 2009.
Military spokesmen have denied reports Bama was overrun by heavily armed militants earlier this week after they attacked it with captured military vehicles and pick-up trucks mounted with machine guns, all part of a growing Boko Haram arsenal.
"Bama today is the centre of the military battle with the terrorists ... Boko Haram is being repelled by the Nigerian troops as we are talking now," the government official said, without giving details of the operations or casualties.
Nigeria's air force and defence headquarters did not respond to requests for comment and it was not immediately possible to obtain independent confirmation of the fighting.
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The battle over Bama, and Boko Haram's storming of towns and villages to the north, east and south of Maiduguri in recent weeks, has raised fears of an attack on the Borno state capital, prompting hundreds of civilians to flee.
"Even today, we can see so many people leaving ... the buses are going out plenty now," Musa Sumail, a human rights activist in Maiduguri who reports on the violence in the northeast, told Reuters. He said he had seen at least one or two Nigerian government fighter jets in the skies above Maiduguri.
Boko Haram, whose leader Abubakar Shekau last month declared a "Muslim territory" in the northeast after capturing the town of Gwoza on the Cameroon border, is believed to be trying to mimic the example of Islamic State (IS) in Syria and Iraq which announced the creation of a separate caliphate there.
Jonathan's government, which faces an election in February, has come under sharpening public criticism for its apparent inability to check Boko Haram's five-year insurgency, which has ravaged the poor northeast corner of Africa's biggest economy.
The group has also claimed shootings and bombings across the north and, more sporadically, in the federal capital Abuja and even in the southern commercial hub Lagos. The attacks have not reached the southern oilfields of Africa's No. 1 crude producer.
The United States is among several western allies helping Nigeria's military with training and intelligence support. This was stepped up following international outrage over Boko Haram's brazen abduction in mid-April of more than 200 teenage schoolgirls in the northeast. The girls are still missing.
In a speech to a security meeting in Abuja on Thursday, the top U.S. diplomat for Africa said Bama's "apparent capture" by Boko Haram and the threat of an assault on Maiduguri was a "sober reality check" for Nigeria and its allies.
"We are past time for denial and pride," Assistant Secretary of State for African Affairs Linda Thomas-Greenfield said, adding that Shekau's announcement of an IS-style "caliphate" showed how much the Nigerian security situation had worsened.
U.S. officials say more extensive security cooperation has been hampered by persistent allegations of human rights abuses levelled against Nigeria's army, which it denies, and Nigeria's sensitivity about outside meddling in its affairs.
"The reputation of Nigeria's military is at stake," Thomas-Greenfield said, pledging U.S support for a border security initiative involving Nigeria's neighbours Cameroon, Chad and Niger which will try to prevent Boko Haram from extending its control over these remote frontier zones of the lower Sahel.
The Sunni jihadist movement, whose name means "western education is forbidden", has killed thousands since launching an uprising in 2009. Counter-terrorism experts say links exist between it and other Islamist groups, such as al Qaeda's North African franchise and Somalia's al Qaeda-linked al Shabaab, but there has been little evidence so far of extensive cooperation.
In Nigeria's February polls, southerner Jonathan is expected to seek re-election. Many believe political tensions stemming from the historic rivalry between Nigeria's mostly Muslim north and largely Christian south is also stoking the violence.