Prime Minister Tony Blair has condemned the killing of a leading Christian Lebanese minister who was shot dead in the country's capital, Beirut.
Mr Blair said the killing was without justification
Pierre Gemayel's death comes amid a political crisis in Lebanon, after six pro-Syrian cabinet members resigned.
Mr Blair said: "We condemn this murder utterly. It is completely without any justification at all."
US Under-Secretary of State Nicholas Burns said the killing was "an act of terrorism" and "intimidation".
Mr Gemayel, a member of the Phalange Party and the son of former President Gemayel Amin, was shot in his car and died later in hospital.
Mr Blair said: "We need to do everything we can, particularly at this moment, to protect democracy in Lebanon and the premiership of Prime Minister Siniora.
"And it underlines once again the absolute and urgent need for a strategy for the whole of the Middle East, that supports those who favour democracy and the proper way of resolving disputes everywhere."
The news of the killing was confirmed by the son of Rafik Hariri, the former prime minister was killed last year in a huge blast.
A recent UN report implicated Syria in Rafik Hariri's death, although Syria has denied involvement.
Gemayel's death is the latest in a series of assassinations in Lebanon
His son, Saad, who is also the leader of the anti-Syrian coalition which has a majority in parliament, has now accused Damascus of being behind the killing of Mr Gemayel as well.
"The Cedar Revolution is under attack...Today one of our main believers in a free democratic Lebanon has been killed. We believe the hand of Syria is all over [this]," he told CNN.
But Syria denounced Mr Gemayel's assassination, calling it a "despicable crime".
"Syria strongly condemns the killing", the official Syrian news agency, Sana, said.
UK Foreign Secretary Margaret Beckett said the killing would increase regional tension.
"Clearly we condemn it. We are dismayed. There are enough problems in Lebanon already," she told a press conference in London.
Shadow foreign secretary William Hague said the Conservatives also "strongly condemned" the killing.
He added: "The international community must support prime minister Siniora's government, as it stands up to this act of intimidation and terrorism."
For the Liberal Democrats, Michael Moore said: "This tragic assassination will further destabilise the political situation in Lebanon."
He added: "This tragedy has the potential to bring further crisis to an already troubled region. We urge all sides to show restraint."
Six pro-Syrian ministers quit their jobs last week in an attempt to bring down the government after their calls for a greater role were rejected.
Despite the resignations, the depleted cabinet approved draft UN plans for setting up an international tribunal to try suspects in Mr Hariri's killing.