"Coordinated air and land operations are being conducted now," Defense Ministry spokesman Brig Gen Chris Olukolade said in a message posted on Twitter.
Troops blocked roads leading into the city, which also is preventing civilians from escaping.
"We believe hundreds of thousands of civilians are now at grave risk," Amnesty International said.
The attacks come the day US Secretary of State John Kerry is expected in Lagos, Nigeria's commercial capital nearly 1,000 miles (more than 1,500 kilometres) southwest of Maiduguri.
Jonathan made a surprise visit to Maiduguri 10 days ago and pledged to crush the insurgents. But his repeated promises are ringing hollow as Boko Haram since August has seized and kept control of large swaths of the northeast, including key border crossings into Cameroon, Chad and Niger.
Boko Haram has denounced democracy and is fighting to impose its strict version of Shariah law across Nigeria, whose population of about 170 million is divided almost equally between Muslims in the north and Christians in the south.
He said he saw dozens of combatants killed. A hospital worker said they are treating dozens of wounded soldiers. Both men spoke on condition of anonymity because they are not authorised to speak to the press.
Boko Haram on January 3 seized a key military base and town on the border with Cameroon, killing hundreds of civilians and leaving the main road open to Maiduguri.
The military said they were counter-attacking a week ago. But escaping civilians said there was no fighting and the insurgents retain control of the town of Baga.
While soldiers were succeeding in holding off the attack on Maiduguri, it appeared they might lose Monguno, according to Abbas Gava, a spokesman for the civilian self-defense groups fighting Boko Haram.
Maiduguri is the birthplace of Boko Haram and has been attacked many times in the five-year Islamic insurgency that killed 10,000 people last year.
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
