Tony Blair has condemned the murder of Lebanese industry minister Pierre Gemayel in Beirut, saying it was "completely without any justification".
The Christian minister, a strong opponent of Syria's influence in his country, was gunned down in his car in the Lebanese capital earlier today. He was taken to hospital but died before he arrived.
The assassination comes amid a political crisis in Lebanon, which is already suffering the aftermath of the war between Israel and Hizbullah this summer. Six pro-Syrian members of the government resigned last week in an attempt to force change.
"I condemn this murder utterly, it is completely without any justification at all. We need to do everything we can, particularly at this moment, to protect democracy in Lebanon and the premiership of prime minister Siniora," Mr Blair said.
"And it underlines once again the absolute and urgent need for a strategy for the whole of the Middle East which supports those who favour democracy and the proper way of resolving disputes everywhere."
US undersecretary of state Nicholas Burns said he was "shocked" by the news, adding: "We view it as an act of terrorism and we also view it as an act of intimidation."
Last week, in the absence of the six ministers who resigned, the Lebanese government approved draft UN plans for an independent tribunal into whether Syria was responsible for the death of former prime minister Rafik al-Hariri last year.
Following news of Mr Gemayel's death today, Mr al-Hariri's son, Saad, who leads the anti-Syrian coalition in the Lebanese government, again pointed the finger towards Damascus.
"The Cedar revolution [which ended Syrian occupation of Lebanon] is under attack," he told CNN, adding: "Today one of our main believers in a free democratic Lebanon has been killed. We believe the hand of Syria is all over [this]."
British foreign secretary Margaret Beckett said: "We are dismayed. There are enough problems in Lebanon already and we hope very much that whatever lies behind this, that it is a one off.
"This is the kind of step that can only increase tension in the region rather than lead to greater peace, and obviously from that point of view it's something that we deplore it."
Her Israeli counterpart, Tzipi Livni, said: "The news from Lebanon is another example of the kind of region, the kind of neighbourhood we are living [in]. This is another support for what I tried to explain before - this is between moderates and extremists."
She indicated Syria was involved in the assassination. However, Damascus has condemned the murder as a "despicable crime", with the country's news agency, Sana, reporting: "Syria strongly condemns the killing."
The Conservatives and the Liberal Democrats both condemned Mr Gemayel's killing, and Lib Dem foreign affairs spokesman Michael Moore urged all sides to "show restraint" and avoid bringing "further crisis to an already troubled region".