David Cameron has defended his decision to speak out on the eurozone crisis, saying it would be "dangerous" for him to stay silent.
The prime minister has irritated some eurozone leaders with his increasingly strident calls for them to take decisive action to end the turmoil in the single currency bloc.
But speaking at the Nato summit in Chicago, he insisted he was entitled to intervene as British interests were at stake, even though the UK is not a member, the Press Association reported.
"What happens in the eurozone matters to the United Kingdom," he said.
"My judgment is that staying silent on these problems would actually be more dangerous than speaking out because we need these issues to be resolved.
"The truth is that we still haven't done enough to decisively resolve the crisis."
Mr Cameron said he had consistently sought to put forward solutions, and not simply criticise other leaders.
"I would argue that the British contribution to this debate has been constructive. We haven't just said 'sort it out'. We have consistently set out the things that need to be done," he said.