Mobile phone giant MTN fuelled the Islamist-led insurgency in Nigeria by failing to disconnect unregistered SIM cards, the Nigerian president has said.

Muhammadu Buhari made the comment during a visit to Nigeria by his South African counterpart Jacob Zuma.

Last year, Nigeria fined the South African-owned firm $3.4bn (£2.7bn) for missing a deadline to disconnect cards.

Nigeria believes Boko Haram militants use unregistered SIM cards to co-ordinate attacks.

BBC Nigeria reporter Martin Patience says fine has overshadowed talks in the capital, Abuja, between the leaders of Africa’s two largest economies.

“You know how the unregistered SIM cards are being used by terrorists and between 2009 and today, at least 10,000 Nigerians were killed by Boko Haram,” President Buhari said at a joint press conference with Mr Zuma.

Other mobile phone operators complied with a mid-2015 deadline to register all SIM cards, but “unfortunately, MTN was very very slow and contributed to the casualties”, Mr Buhari added, in his first comments on the issue.

Nigeria initially imposed a $5.2bn fine on MTN in October, but brought it down to $3.4bn.

Mr Buhari said MTN, which was in talks with Nigeria to reduce the fine further, could make gradual payments, Reuters news agency reports.

Last month, MTN said it had dropped court action to challenge the fine, and had paid $250m as part of efforts to reach an “amicable settlement”.

MTN has 231 million subscribers in 22 countries across Africa, Asia and the Middle East. However, Nigeria is its biggest market.

In September, the company was named as most-admired brand in Africa in the Brand Africa 100 awards, beating Samsung, while it was also awarded the continent’s most valuable brand, worth $4.6bn.

MTN was South Africa’s second mobile operator when it was set up in 1994 after the end of apartheid.

It began its expansion across Africa four years later with operations in Rwanda, Uganda and Swaziland.

The six-year insurgency in north-eastern Nigeria has killed some 17,000 people and forced more than 2.6 million from their homes.

Mr Buhari said in December that Boko Haram was “technically” defeated but attacks have continued.

Meanwhile, President Zuma has called for collaboration between South Africa and Nigeria in areas that would promote peace and security on the continent. He thanked Nigeria for her role in dismantling apartheid. Zuma who also addressed a joint National Assembly said both countries shared common values and history.

In his response, Speaker of the House of Representatives, Yakubu Dogara, called for more respect from South African authorities and people for Nigeria and Nigerians.

“South Africa has a large population of Nigerians living and contributing their quota to its development. We, as representatives of the people seek that this brotherhood between our leaders translates to good relations between citizens of both countries and it is only then that both countries can speak to true integration of our peoples in the interest of our continent.

“May I also seize this opportunity to commend President Jacob Zuma as well as the South African Investors for their interest and confidence in taking advantage of the robust investment opportunities in our country especially now the current administration has brought corruption to its knees. We (both corporate and individuals) look forward to better reciprocal treatment of our citizens in South Africa”, Dogara said.

Additional Reports from BBC.