The NATO Secretary-General Anders Fogh Rasmussen has said the organisation is ready for any challenges "from where they come". Mr Rasmussen was speaking at the Welsh summit of NATO leaders.

It comes as they meet about how to deal with Russia, and its involvement in the conflict in eastern Ukraine.

Mr Rasmussen said the gathering would forge a stronger NATO "for a more complex and chaotic world" during an address in Newport.

It will be attended by the alliance's 28 heads of state and government.

Mr Rasmussen said the alliance is on track to take important decisions to make NATO faster, fitter and more flexible - so that it can meet current and future security challenges.

Britain is expected to use the summit to make the case for increased defence spending, something US President Barack Obama is also calling for.

British Prime Minister David Cameron said: "It's hard to think of a NATO summit coming at a more important time for our alliance.

"We see the appalling actions of Russia in eastern Ukraine. We see the appalling scenes in Iraq and Syria and the rise of this so-called Islamic Caliphate and its dreadful brutality in executing the American hostage we saw overnight."

"And in this dangerous and difficult world NATO has an absolutely key role in providing our collective security, and that's what the next two days are going to be all about," he added.

Russia's military aggression against Ukraine - as well as growing instability to the South, including the rise of extremism and sectarian strife in the Middle East and North Africa - are expected to top the summit agenda.

They will also focus on newer threats such as cyber, missile defence and hybrid warfare.

Mr Rasmussen says the current situation between Russian and Ukraine should be seen as a wake-up call for Europe.