Nigeria's militant group Boko Haram remains a threat, French President Francois Hollande has warned ahead of a summit in Nigeria's capital, Abuja.

This was the case despite "impressive" gains against the group, Mr Hollande said after meeting his Nigerian host Muhammadu Buhari.

Leaders of countries making up a force against the Islamist group are among those attending Saturday's summit.

The group's seven-year insurgency has killed some 20,000 people.

More than two million have been displaced from their homes.

Boko Haram militants have been attacking civilian targets as the Nigerian military seeks to wrest territory from their control.

The group has established links with so-called Islamic State (IS), after pledging allegiance to it in 2015.

President Muhammadu Buhari is welcoming counterparts from Benin, Cameroon, Chad and Niger for the gathering in Abuja, along with French President Francois Hollande, UK Foreign Secretary Philip Hammond and US Deputy Secretary of State Antony Blinken.

Mr Blinken - who is already in Nigeria - said he was concerned by reports that Boko Haram militants were going to Libya, where IS influence has grown in recent months.

"We've seen that Boko Haram's ability to communicate has become more effective," he said.

"They seem to have benefited from assistance from Daesh [IS]."

At the same time, he declined to comment on whether the US would agree to a Nigerian request to sell it American war planes to fight Boko Haram.

After meeting President Buhari ahead of the summit, Mr Hollande praised his host and the regional countries for their co-ordination, adding that France provided "intelligence, information, training and equipment".

"It is this cohesion, this solidarity, this strategy which has enabled the success we are witnessing," he said.

The UK foreign secretary said Britain was training 1,000 Nigerian soldiers to attack Boko Haram strongholds in the north-east.

Mr Hammond said the Islamist group was being "degraded", adding: "We must maintain the momentum to win the war, and build the right conditions for post-conflict stability in the region".