Regrettably, Luke was not present, though hostages of other nationalities were present and were rescued," the National Security Council said.

A man identifying himself as Luke Somers, who was abducted in 2013, has appeared in a video, saying his life is in danger and appealing for help.

The video also shows a member of al-Qaeda in the Arab Peninsula (AQAP) threatening to kill Mr Somers unless unspecified demands are met.

Mr Somers, 33, worked as a journalist and photographer for local news organisations and his material appeared on international news outlets, including the BBC news website.

Analysis by Aleem Maqbool, BBC News, Washington

The US saw an opportunity to rescue one of its civilians and took it. But the risk was that failure would put the hostage in further danger. In this video, al-Qaeda in the Arab Peninsula says this is exactly what has happened.

Scrutiny of US policy on dealing with kidnappers has increased with the deaths of three Americans held by Islamic State militants in Syria - each paraded on video, threatened and then beheaded.

The Obama administration has been criticised for not paying ransoms, not allowing hostage families to speak out and not taking opportunities to negotiate.

While the White House stands by its policies, the president has ordered a review.

With its videos and killings, Islamic State has achieved its objectives of spreading fear and gaining notoriety, and this new video from Yemen suggests its propaganda is inspiring other groups.

On 25 November, US and Yemeni forces rescued six Yemenis, a Saudi and an Ethiopian being held by AQAP in an operation at a mountain cave in the remote Hajr al-Sayar district of Hadramawt province. Seven militants were reportedly killed.

US National Security Council spokeswoman Bernadette Meehan said: "As soon as the US government had reliable intelligence and an operational plan, the president authorised the department of defence to conduct an operation to recover Mr Somers."

 The lack of any angry reaction has been significant, but there is no guarantee that will remain the case should England get even one bad result in Euro qualifierschina virtual office.

If Hodgson does not stay in his post through to 2018 - and it is hard to see he will - the FA will then have a difficult choice because, while there have been crucial junctures for England before, this seems even more important given the scale of their failure in Brazil.
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England captain Steven Gerrard Sim

The received wisdom seems to be that the national manager should now be English and interlocked with the work at the National Football Centre at St George's Park.

This would suggest that, unless a new and emerging contender comes through, next man in line to succeed Hodgson would be either current coach Gary Neville or Gareth Southgate, who is in command of the under-21 side.

Should this be the case? Should the FA simply go English for English sake if a better alternative is available?

Chelsea manager Jose Mourinho flirted with the FA before and the fluid nature of his career means his path is not easy to map out. But his only national interest is Portugal and much later in his career.

QPR boss Harry Redknapp and BBC Sport pundit Alan Hansen have both mentioned Liverpool manager Brendan Rodgers and Everton's Roberto Martinez as potential England managers. As one is from Northern Ireland and the other is a Catalan, they may not fit the brief, even if they actually wanted the job hair loss treatment.

But now experts at the International Institute for Strategic Studies (IISS) in London have told the BBC that they have identified a Russian tank in a separatist column in eastern Ukraine that they say could only have come from across the border in Russia.

Joseph Dempsey, an IISS analyst, has studied video footage reportedly taken on 26 August in Sverdlovsk, Luhansk, in eastern Ukraine. The video shows a convoy of military vehicles.

Whilst date and location are unconfirmed, he says the operator of the convoy is apparent: flags associated with the separatist movement are clearly displayed and some vehicles feature bright green areas, a common feature of separatist armour.

The mixed convoy includes at least three T-72B1 Main Battle Tanks (MBTs) but it is the appearance of a lone, more modern T-72 variant (shown below) that is of particular significance.
A screengrab from the video footage analysed by IISS - 26 August 2014

This variant, distinguished by the prominent Kontakt-5 Explosive Reactive Armour (ERA) arrangement - the boxes on the turret front - is commonly referred to by Western sources as the T-72BM.

It is operated by the Russian Army in large numbers, but crucially it is not known to have been exported or operated outside of Russia.

According to the IISS, the presence of this variant in Ukraine therefore strongly supports the contention that Russia is supplying arms to separatist forces.

Up to now deniability has been a key-note of Moscow's "ambiguous war" strategy in eastern Ukraine.

The IISS says that the first separatist tanks observed were identified as T-64BV, a variant constituting the majority of the Ukrainian army fleet.

It was therefore initially assumed that they, like separatist armoured vehicles before, had been captured in engagements with government forces or through access to known army depots within contested areas.