Western leaders have criticised Russia for its "destabilising" influence on the crisis in Ukraine, at the start of a Nato summit in Wales.

Nato and the UK warned that pressure on Russia would be increased if it did not change course in eastern Ukraine.

Ukraine's president is to brief US and EU leaders on earlier discussions on a ceasefire plan with Russia's President Vladimir Putin.

Some 2,600 people have died in fighting between Ukrainian troops and rebels.

The West says it has evidence that Mr Putin is supporting the separatists with training and arms, but Russia denies this.

The conflict has forced more than a million people from their homes in eastern Ukraine, according to latest United Nations estimates.

The two-day Nato summit in Newport will be dominated by the crisis in Ukraine.

But leaders are also set to discuss the rise of Islamic State (IS), and Afghanistan where Taliban militants launched a deadly attack on a government compound on Thursday.

Writing in the Times, UK Prime Minister David Cameron and US President Barack Obama said they would "confront" IS, warning their countries would "not be cowed by barbaric killers".

Their statement comes following the release of a new IS video showing the killing of US journalist Steven Sotloff, just days after the group beheaded another American reporter, James Foley.

In the latest video, an IS militant is also seen threatening to kill a UK hostage.

Russian actions 'unacceptable'

On Thursday, Nato Secretary-General Anders Fogh Rasmussen said the summit was taking place in a "dramatically changed security environment", with Russia "attacking Ukraine".

"We are still witnessing unfortunately Russian involvement in destabilising the situation in eastern Ukraine," he told journalists in Newport on Thursday ahead of the summit's official launch.

Mr Cameron stressed pressure of sanctions was "the right way to tell the Russians that what they are doing is unacceptable".

The BBC's Bridget Kendall says the summit is Nato's most important for decades, as leaders faced the question of whether the alliance is equipped to deal with 21st century challenges.

The alliance is expected to approve plans to create a rapid response force composed of several thousand troops from member states, able to deploy within 48 hours.

European leaders are also set to discuss a new round of tougher economic sanctions on Russia.

Source: BBC