The UK has followed the US in despatching an official envoy to try to help resolve the crisis in Libya, the scene of escalating fighting and tensions, by promoting dialogue between rival factions.

David Cameron's choice is Jonathan Powell, a former career diplomat and senior aide to Tony Blair, architect of the western reconciliation with Muamar Gaddafi when he was prime minister a decade ago. Powell held a first exploratory meeting with Libya's prime minister and different groups in Tripoli last month, the Foreign Office confirmed on Friday.

The US emissary, whose appointment was announced this week in Washington, is David Satterfield, a senior ambassador with extensive Middle Eastern expertise.

The EU, France, Germany, Italy, the UK and US all expressed their deep concern about Libya in a statement on Friday. "We stand ready to support an inclusive reconciliation process in order to gather all the Libyans in support of the political transition, with the support of the United Nations." they said, warning of "chaos, fragmentation, violence and terrorism," if reconciliation failed.

France, the EU and the Arab League have also announced the appointment of envoys to Libya in the last few days - reflecting mounting international and regional alarm about the crisis.

Powell has long experience of conflict resolution from his time working on the Northern Ireland peace process and in recent years has undertaken mediation efforts in Colombia and Bahrain. He was Blair's chief of staff in the runup to the Iraq war in 2003.

Cameron is said to be increasingly concerned about the chaotic outcome of the 2011 Nato intervention in Libya in which he and the French president, Nicolas Sarkozy, played central roles. Downing Street said Powell had gone to Libya "at the request of the UK government".

The missions were announced after discussions about Libya in the margins of a London conference about Syria last week. That brought together US secretary of state John Kerry, the UK's William Hague and counterparts from France, Germany and Italy. The different envoys would all work "in concert", Kerry said.

"Powell was asked to look at the situatoin on behalf of the prime minister and to report back as to whether he thought this was worth doing, along with the US," a Whitehall source said. "The idea is to try and push and cajole the Libyans towards an agreement." The UK is already helping train Libya's armed forces and improvig government capacity as part of a process of state-building. But the view is that these will not help unless fundamental political disagreements can be resolved.

Tensions exploded this week when forces loyal to a renegade general, Khalifa Haftar, attacked the parliament in Tripoli and miltiants of the extremist Ansar al-Sharia group in Benghazi, against a background of increasing polarisation between nationalists and Islamists and mutual accusations about betraying the 2011 revolution that overthrew Gaddafi. The US and Britain both insist that they are not supporting Haftar - who was backed by the CIA in the 1980s — and are working to promote national reconciliation.

Powell and Satterfield are expected to make a joint visit to Tripoli in the coming weeks. Powell faced criticism over family connections to Libya in 2009, when it was revealed that his brother, Lord Powell, who was foreign policy adviser to Margaret Thatcher, was chairman of a company that was building hotels in Libya while Gaddafi was still in power.