“Your alliance will not achieve anything. Amass all your weapons and face us. We welcome you,” he said in a 28-minute speech, in one of the three videos posted by the sect on YouTube.
Troops from Nigeria have been backed by soldiers from Chad, Cameroun and Niger in recent weeks because of increased concerns about Boko Haram’s threat to regional security.
In the second of the latest videos, images of the leader of the Islamic State group, Abu Bakr al-Baghdadi, are shown along with archive footage and a voiceover recalling a battle between British colonial soldiers and fighters from the Sokoto Caliphate in northern Nigeria.
Shekau has name-checked al-Baghdadi before but appears to be positioning Boko Haram in a wider jihadi context by showing the Sokoto Caliphate, which was dismantled by the British in the early 20th century.
“We never rose up to fight Africa. We rose up to fight the world,” he said.
“We are going to fight the world on the principle that whoever doesn’t obey Allah and the Prophet to either obey or die or become a slave.”
On Sunday, Boko Haram militants waged twin attacks on the town of Diffa in southeast Niger, opening a new front in its offensive after repeated attacks on Cameroun’s far northern region.
The six-year uprising has become a regional crisis and on Saturday, Nigeria, Chad, Niger, Cameroun and Benin agreed to muster 8,700 troops, police and civilians to fight the group.
But Shekau dismissed the size of the force, which had previously been set at about 7,500.
“You send 7,000 troops? Why don’t you send 70 million? This is small. Only 7,000? By Allah, it is small. We can seize them one-by-one. We can seize them one-by-one,” he said in Arabic.
Shekau also directly threatened Chad’s President Idriss Deby, whose forces have attacked Boko Haram in the northeast Nigerian towns of Gamboru and Malam Fatori in recent days.
In the videos, Shekau first spoke in Arabic and later translated in Hausa, vowing to continue attacking and killing those he described as “infidels”.
In the first video, the sect leader appeared in combat gear in front of Hilux vehicles mounted with anti-aircraft guns and an AK47 rifle on his shoulder. He was between two masked men who were both holding AK47 rifles.
Seen reading a prepared text, Shekau insisted that the alliance forces would not deter the group from carrying out its rein of violence across the region.
He also vowed to ensure that the sect hampers the progress of democracy and continues the mission of Islamisation of not only Nigeria, but her neighbouring countries.
Also, in the second video, armed men were shown punishing those who “violated” Islamic laws, two young men were seen receiving lashes for “commiting adultery”.
Similarly, the video showed another man whose right hand was being amputated for “stealing”, while a third who was shown being stoned to death for “fornication” had his entire body with the exception of the head buried in a ditch.
Also shown were hundreds of people, including women adorned in hijabs and children with hundreds of Boko Haram fighters chanting "Allahu Akbar", meaning “God is Great”, driving towards an unknown destination on a deserted highway.
In the third video clip, the sect featured the “temporary” invasion of Damaturu, the capital of Yobe State on December 1, 2014. In the video, hundreds of insurgents in a convoy of utility vehicles and motorcycles were led by an armoured personnel carrier driven through Gujba road.
They later emerged in front of the Yobe Government House along Maiduguri road where an exchange of gunshots ensued before they got access into the premises.
An unidentified spokesman, surrounded by hooded fighters later appeared in a bush where he showcased over 50 vehicles and ammunition, which he said were the “spoils of war” they got from Damaturu.
He also debunked claims by the Nigerian armed forces that the December 1 attack by the group on Damaturu was repelled, insisting: “We had a field day in Damaturu, ate and dined, took what we wanted and thereafter drove out of the town at our own volition, with all the vehicles, ammunitions and other things we wanted to take along.”
Meanwhile, Boko Haram members launched a new attack on neighbouring Niger yesterday, as the country’s parliament in Niamey was set to vote on joining a regional force against the terror group, AFP reported.
The insurgents raided a prison in the southeastern border town of Diffa but were repelled after a heavy exchange of fire, humanitarian sources said.
“The attack failed. The assailants were quite easily pushed back,” one source told AFP.
No casualty toll was immediately available after the raid by Boko Haram.
A journalist in Diffa said he saw the bodies of Boko Haram fighters in a hearse despatched by the town hall, but he was unable to count them.
Some Boko Haram fighters sought to hide out in the town.
“The soldiers are looking for them, weapons at the ready. The army has encircled Diffa,” the journalist said.
Another journalist said some of the fighters were being held in the prison they attacked.
Niger’s parliament was expected to support a proposal to deploy troops inside Nigeria to help in the battle, along with soldiers from Chad and Cameroun.
In another incident, suspected members of the Islamist group also hijacked a bus in northern Cameroun, abducting at least 20 people, residents said yesterday.
The insurgents reportedly seized a bus carrying market-goers and drove it towards the border with Nigeria.
Some reports put the total number kidnapped in Cameroun as high as 30.
The bus was seized near the border area of Koza and driven towards the Nigerian border 18km (11 miles) away, a resident told the Associated Press (AP) news agency.