By Andrew Osborn
LONDON (Reuters) - British Prime Minister David Cameron's government on Thursday accused the Labour party of "giving succour" to Syrian President Bashar al-Assad, after the opposition party made clear it would not support an imminent military strike against Syria.
In a move that deepened a widening split that threatens to complicate Cameron's efforts to secure bipartisan backing for military action, the defence secretary and Cameron's head of communications leveled the charge at Labour leader Ed Miliband.
"I am disappointed with Ed Miliband's behaviour frankly," British Defence Secretary Philip Hammond told Channel 4 TV news.
"Anything that stops us from giving a clear, united view of the British parliament tonight will give some succour to the (Assad) regime."
Hammond was speaking as Britain's parliament debated how Britain should respond to a suspected chemical weapons attack in Syria as lawmakers from across the political spectrum aired deep unease about the prospect of military strikes.
Earlier on Thursday, Craig Oliver, Cameron's head of communications, had complained to reporters that "a lot of the arguments over this could give succour to the (Syrian) regime".
Labour complained to Britain's top civil servant Jeremy Heywood over what it said were "infantile" and "irresponsible" comments, demanding an apology and asking for the comments to be withdrawn.
"It is particularly disappointing given the serious nature of today's debate and the fact that throughout the country people will be listening with great concern about events in Syria, some knowing their relatives could soon be involved in military action," senior Labour MP Michael Dugher wrote in a letter to Heywood.
Cameron was forced to change tack on Wednesday evening and extend his timetable for military action against Syria after Miliband threatened to sabotage a parliamentary vote on the subject.
In a breach of etiquette that exposed unusual rancour within Britain's political elite, an unnamed person in Cameron's office used a string of strong expletives on Wednesday night to describe to the Times newspaper what the government thought of Miliband, which the paper duly published on Thursday.
(Additional reporting by Marie-Louise Gumuchian; Editing by Sonya Hepinstall)