US secretary of state John Kerry refused to endorse Nigeria claims that Boko Haram leader has been wounded.

US Secretary of State John Kerry (L) meets with the Sultan of Sokoto Muhammadu Sa'ad Abubakar at his palace in Sokoto, on August 23, 2016 ©Pius Utomi Ekpei (AFP)

US Secretary of State John Kerry on Tuesday praised Nigeria for its recent gains against Boko Haram Islamists but did not endorse military claims that the group's leader Abubakar Shekau has been wounded.

Speaking at a press conference in the ancient northern city of Sokoto, Kerry congratulated Nigeria for reclaiming swathes of territory and releasing thousands of hostages from Boko Haram while warning against the use of excessive force to fight extremists.

Nigeria has made "important progress", Kerry said. "Nigeria and its neighbours are degrading Boko Haram's capabilities."

But the top US diplomat cautioned against a heavy-handed response and emphasised respect for human rights.

"It is understandable that, in the wake of terrorist activity, some are tempted to crack down on anyone and everyone who could theoretically pose some sort of threat," Kerry said.

"But extremism can't be defeated through repression or fear. Fear instilled through repression invites not confidence but contempt," Kerry said, "it creates terrorists, trust creates citizens."

His cautionary message came hours after Nigeria's military claimed to have hit the elusive Shekau in an airstrike on the Islamist group's forest stronghold, saying he was "fatally wounded on his shoulders" during an "unprecedented and spectacular" Friday raid.

The army has not provided any further evidence that Shekau was wounded.

- 'Strong start' -

Nigeria has repeatedly claimed to have killed Shekau in previous raids only for the leader to surface shortly afterwards in videos.

Steering clear of any potential embarrassment, Kerry made no mention of the claim that Shekau -- Boko Haram's leader since 2009 -- had been wounded and did not take questions from the press.

This week Kerry is on a three-nation tour focussed on counterterrorism that sees him visiting Kenya, Nigeria and Saudi Arabia.

His meetings have focussed on defeating the terrorist threats across the continent, from Al-Qaeda-affiliated Al-Shabab in East Africa to Islamic State-backed Boko Haram in the West.

"You have made a strong start at all levels of government," Kerry said about Nigerian President Muhammadu Buhari.

The much-needed support comes as Nigeria is heading into a likely recession and is wrestling with a growing humanitarian crisis in the north.

In Sokoto, Kerry urged Nigerians to transcend "religions, ethnicities and all kinds of moral codes" by practising "tolerance and acceptance" to build unity and defeat terrorism.

- 'Rebuilding trust' -

The previous day, in northern Zamfara State, eight people were burned to death by a mob after a Muslim man tried to help a Christian accused of blasphemy.

To change the situation requires "rebuilding trust in the government", Kerry said, assuring that the White House would continue to provide military and humanitarian support to Nigeria, a country home to over 170 million that is struggling to provide for people in its war-torn north.

Earlier this month the US government pledged $37 million in aid for victims of Boko Haram as fears of a famine mounted in the ravaged Lake Chad region.

Kerry said that the US will partner with Nigeria to open temporary schools where "displaced children are given access to meals, counselling and other social services."

In its quest to create a fundamentalist Islamic state, Boko Haram has killed more than 20,000 people and displaced 2.6 million from their homes.

With entire villages razed to the ground and fertile farmlands abandoned, the United Nations has warned that some 50,000 children could starve to death this year in Borno state alone if nothing is done.

On Wednesday Kerry is scheduled to meet representatives of local non-government organisations to fight against corruption -- a priority of the Buhari administration -- before flying to Saudi Arabia where he will discuss the Yemen crisis, the war in Syria and the international fight against the Islamic State group.

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