Militant Islamists in Nigeria have released a new video and, unusually, Boko Haram leader Abubakar Shekau fails to appear in it.

Instead, an unidentified young man speaks in the name of "The army of the caliphate in West Africa".

Mr Shekau's absence from the video has fuelled speculation about his fate.

At least 13 people were killed on Tuesday in a bombing at a cattle market in Maiduguri city, a former Boko Haram stronghold in north-eastern Nigeria.

In the 10-minute video, the speaker dismisses as a lie the Nigerian military's assertion that it has recaptured all cities and towns from the militants.

He shows the identity cards of government troops he says have been killed, and the wreckage of what he describes as a jet that had been brought down.

BBC Nigeria analyst Naziru Mikailu says the video appears to be a genuine Boko Haram production.

The fact that it was issued under the banner of "The army of the caliphate in West Africa" reflects that the group is now allied with Islamic State (IS) militants fighting for a global caliphate, he says.

Abattoir explosion

However, Mr Shekau's absence from the video, and the failure to mention him, is surprising, our correspondent adds.

It suggests a split in Boko Haram or one of three other possibilities:

• Mr Shekau has been wounded
• He has been killed or
• He has gone deep into hiding, making it difficult for him to appear in the video.

The speaker, who was carrying a rifle and whose face was covered, said the video was shot in Sambisa, a vast forest surrounding a game reserve.

The group controlled the forest, and was running education projects - ranging from studies about Islam to technology - for people under its rule, he said.

Meanwhile, Red Cross officials said that at least 13 people were killed and 24 wounded in the latest bombing in Maiduguri, the biggest city in north-eastern Nigeria.

The bomb went off in the abattoir section of the cattle market.

Overnight the militants fired grenades at people's homes in Maiduguri, reports the BBC's Nigeria correspondent Will Ross.

Last Saturday, 29 people were killed in Maiduguri when a mosque was bombed.

Nigeria's new President Muhammadu Buhari, a Muslim, has described Boko Haram as "mindless" and "godless".

He said the military command centre would be relocated to Maiduguri and remain there until the group was completely subdued.

He is due to meet the presidents of neighbouring states later this week to improve the regional military offensive against the jihadists.

About 1.5 million people have been displaced and hundreds more abducted since the group launched their violent uprising in 2009.

More than 15,500 people have been killed in the fighting.