Defence Secretary Philip Hammond accused Opposition leader Ed Miliband of giving "succour" to the Assad regime as the Westminster battle over potential military action in Syria became increasingly bitter.
Mr Hammond said Labour's decision to oppose a Government bid to secure MPs' support in principle for an armed response to chemical weapons use could encourage the Syrian government.
"Anything that stops us from giving a clear united view of the British Parliament tonight will give some succour to the regime," he told Channel 4 News.
Labour earlier lodged a complaint about David Cameron's top spin doctor after he also accused Mr Miliband of potentially "giving succour" to Assad.
International Development Secretary Justine Greening claimed she missed the crucial vote on Syria because she did not hear the division bell
Britain's place in the world changed with last night's Commons vote on Syria, as David Cameron spectacularly misread his own party.
It was clear the majority of MPs would not be prepared to back unilateral action by the US and Britain. Today we need to make clear why.