Winner of Nigeria's presidential election, Muhammadu Buhari, has issued a defiant vow against militants Boko Haram, saying they would "soon know the strength of our collective will".

The president-elect also vowed to tackle corruption, which he described as an "even greater evil".

Gen Buhari won the election beating President Goodluck Jonathan by 2.5 million votes.

World leaders congratulated Gen Buhari and hailed Nigeria's democratic spirit.

Gen Buhari, of the All Progressives Congress (APC), has become the first opposition candidate to win a presidential election in Nigeria.

In a televised speech, he said: "In tackling the insurgency, we have a tough and urgent job to do. Boko Haram will soon know the strength of our collective will. We should spare no effort until we defeat terrorism."

Much of Gen Buhari's support was in the north, in particular the north-east, which has suffered from Boko Haram's six-year insurgency. The militants have killed thousands of people in their drive to establish an Islamic state.

Many people accused Mr Jonathan of not taking Boko Haram seriously and thought Gen Buhari would be better positioned to defeat the militants.

Gen Buhari, 72, also angrily denounced corruption, saying: "It creates unjustly enriched people... and undermines democracy. Corruption will not be tolerated by this government."

He praised his defeated rival, saying: "I extend a hand of friendship and conciliation to President Jonathan and his team. I have no ill will against anyone. He has nothing to fear from me. He is a great Nigerian and still our president."

Pledging to uphold the rule of law, the former military ruler said: "Your constitutional rights remain in safe hands - you will be able to voice your opinion without fear of victimisation."

Gen Buhari pledged a government "that will listen to, and embrace, all", adding that "there shall be no bias or favouritism for any Nigerians".

He said: "Our nation faces many challenges - insecurity, corruption, economic decline. I pledge to give you my best in tackling these problems."