THE crisis in Ukraine is set to be the number one issue when members of the Nato military alliance gather in Newport this September with Afghanistan also on the agenda, according to a top US diplomat.

On Tuesday defence ministers from Nato’s 28 member states will gather for discussions at the organisation’s headquarters in Brussels – the third of four meetings ahead of the Celtic Manor summit on September 4-5.

US Ambassador to NATO Doug Lute told a press conference at the complex on Monday that it was “clear to the alliance that this is the most severe challenge to stability in Europe since the end of the Cold War.”

The Ukraine crisis escalated earlier this year when unmarked armed forces began to be seen in the Crimea region of the country.

The region was then taken over by Russia following a referendum.

It was a move widely condemned in the West, with the UK foreign secretary William Hague at the time calling the annexation a land grab.

Mr Lute said the longer term implications of Ukraine would be discussed by defence ministers this week, and he said: “This is a discussion that will culminate with leaders at the Wales summit the first week of September.”

“Ukraine will now be subject number one,” he said, indicating that Afghanistan was also on the summit agenda and had been before the Ukraine crisis began.

In Afghanistan NATO’s combat mission is due to end in December, with packages of further support likely to be discussed at the summit.

Mr Lute referred to US president Barack Obama’s announcement that almost 10,000 US troops will be committed to Afghanistan from January 2015.

“With that troop announcement several bits of the package for Afghanistan begin to come into focus – with that troop announcement I imagine other allies will begin to finalise their troop commitments,” he said.

“We’ve always talked about this package coming together by Wales, but... now it’s more tangible and concrete,” Mr Lute explained.