Nigeria Bombs Islamists, US Secretary Of State John Kerry Warns President Jonathan

Nigerian warplanes struck militant camps in the northeast on Friday in a major push against an Islamist insurgency, drawing a sharp warning from the United States to respect human rights and not harm civilians.

Troops used jets and helicopters to bombard targets in their biggest offensive since the Boko Haram group launched a revolt almost four years ago to establish a breakaway Islamic state and one military source said at least 30 militants had been killed.

But three days after President Goodluck Jonathan declared a state of emergency in the northeast, U.S. Secretary of State John Kerry issued a strongly worded statement saying: "We are ... deeply concerned by credible allegations that Nigerian security forces are committing gross human rights violations, which, in turn, only escalate the violence and fuel extremism."

The United States is the biggest foreign investor in Africa's most populous nation, notably in its energy sector, and buys a third of Nigeria's oil. Washington "condemns Boko Haram's campaign of terror in the strongest terms", Kerry said, but urged Nigeria's armed forces to show restraint and discipline.

Nigerian defense spokesman Brigadier-General Chris Olukolade said in a statement that troops destroyed several Boko Haram camps and weapons stockpiles in forests around Borno state, epicenter of the uprising and relic of a medieval Islamic empire: "Heavy weapons including anti-aircraft and anti-tank guns were also destroyed in the process," he said.

"The special operations ... resulted in the destruction of much of the insurgents' weapons and logistics such as vehicles, containers, fuel dumps and power generators."

He said the death toll amongst the insurgents would be verified during mopping up exercises in the camps, including in the Sambisa game reserve in Borno state. A military source said at least 30 insurgents had been killed in one operation.

Nigerian forces are trying to regain territory controlled by well-armed militants in remote northeastern stronghold states of Borno, Yobe and Adamawa, put under a state of emergency by President Goodluck Jonathan on Tuesday.

The Islamists, seen as the main security threat to Africa's top oil producer, have been staging bolder attacks since last month, including one on the town of Bama that left 55 dead.

Nigerian authorities fear they are creating an enclave in remote border areas, as al Qaeda linked militants did in the deserts of Mali before the French forced them out in January.

But previous efforts to crush Boko Haram have always proved temporary, forcing them to dissipate into hiding places or across borders, where they wait, regroup and then come back.

The military is already overstretched in the north, by operations against oil theft in the south and foreign missions.

More troops arrived on Friday in the Borno state capital Maiduguri, where Boko Haram was founded as a clerical movement opposed to Western culture, but which after a military crackdown on it killed 800 people, morphed into a full armed rebellion and forged ties with al-Qaeda linked groups in the Sahara.

"I saw more than 20 trucks loaded with soldiers fully kitted for battle towards Marte. I wish them luck in ending this BH (Boko Haram) madness," resident Ahmed Ibrahim said.

A day earlier, 11 trucks of police trained in counter-insurgency had arrived in Maiduguri, security officials said. Mobile phone connections to Borno and Yobe states were cut.

In some parts of Maiduguri, and in Yola, the capital of Adamawa state, traffic returned to roads and shops re-opened, as most military operations took place in remote rural areas. Roads out of the city to such areas were sealed off by soldiers.