NATO leaders convened at a summit in the UK to reiterate their support for Ukraine in its conflict with Russia, and discuss the threat of the Islamic State reports Al Jazeera.

Ukrainian President Petro Poroshenko held talks with US President Barrack Obama and other Western leaders on the conflict with pro-Russian militants in Ukraine.

The NATO chief on Thursday warned that Russian intervention in Ukraine is the most serious security threat in Europe since the Cold War.

The United States vowed justice for the beheading of a second American journalist Steven Sotloff by Islamic State militants, depicting in a video released yesterday.

The video, entitled 'A second message to America', was deemed authentic by US and UK intelligence services.

"Whatever these murderers think they will achieve by killing innocent Americans like Steven, they have already failed," US President Barack Obama said. (See video here)

Nigeria and its neighbours have met to discuss the rapid advance of Boko Haram in the country’s northeast, amidst fears of increased regional instability.

Foreign ministers from Benin, Cameroon, Chad and Niger were joined by officials from the US, Britain, France, Canada, the African Union and the UN, in the one-day meeting, aimed at reviewing progress of earlier meetings, Nigerian officials said on Wednesday.

The meeting would examine "the extent of foreign assistance, including efforts by the Nigerian government, in the continued fight to … rout the Boko Haram insurgency", the Nigerian foreign ministry said, according to The Guardian.

Somalia has offered members of al-Shabab amnesty, a day after a US air strike, which may have killed the leader of the militant group.

Members have been given 45 days to surrender to authorities, in order to be reintegrated into society, a statement by the government said.

US troops landed at the site soon after the strike, which was targeted at the leader Ahmed Abdi Godane, and took away bodies after a fierce gun battle, reported the BBC Somali Service.

Germany is to ship arms to Kurdish forces fighting against Islamic State militants in Iraq, in a historic move which breaks from a longstanding refusal to send arms to conflict areas.

Holding a special session on Monday, German Chancellor Angela Merkel told the Bundestag that "inconceivable atrocities" had been committed.

Over €70 million worth of arms, including guns, grenades and rockets are to be sent, reports The Times.

“We have the opportunity to save lives and stop the further spread of mass murder in Iraq,” Merkel said.

Militants from Boko Haram have captured the strategic town of Bama, the second biggest town in Borno state in Nigeria’s north, local residents told BBC Hausa.

Thousands of civilians and Nigerian soldiers are reported to have fled the town after fierce fighting with Boko Haram.

It is feared that the militants’ next target is the state capital of Maiduguri, 70km northwest of the town, according to BBC Hausa’s Mansur Liman.

Read more here.

Boko Haram last month declared an Islamic caliphate in the areas it controls.

The US military has confirmed it carried out a targeted operation against al-Shabab militants in Somalia.

"U.S. military forces conducted an operation in Somalia today against the al-Shabab network. We are assessing the results of the operation and will provide additional information as and when appropriate," said Pentagon Press Secretary Rear Adm. John Kirby.

A senior Somali intelligence official told AP news agency that the US was targeting the leader of the group, Ahmed Abdi Godane.

Four peacekeepers with the UN mission in northern Mali (Minusma) were killed when their convoy struck a land mine on Tuesday.

“The toll is four dead and 15 wounded, including six very seriously,” Olivier Salgado, spokesperson for Minusma told Reuters.

“This is only a provisional toll because we do not know what will happen with six of the very seriously wounded.”

The Islamic State released a video today that showed the beheading of a US journalist held hostage, Steven Sotloff, reports the BBC.

Sotloff, who disappeared in Syria in 2013, appeared at the end of a video last month which showed the killing of another US journalist James Foley.

The video released today, entitled “A second message to America”, shows a masked figure together with Sotloff.

The Islamic State militant, addressing his speech to the US President Barack Obama said,

“I’m back Obama, and I’m back because of your arrogant foreign policy towards the Islamic State, despite our serious warnings. We take this opportunity to warn those governments that enter the evil alliance of America against the Islamic State to back off and leave our people alone.”

The militant, whose voice also featured in the video of the beheading of US journalist James Foley, is believed to be British.

The video also carries a warning to the UK, that the execution of a British citizen would be next.

A White House spokesperson, though unable to verify the credibility of the video, condemned the Islamic State actions as a “brutal act.”