South West Liberal Democrat MEP Sir Graham Watson has apologised after a tweet suggesting al Qaida had won a victory over the Prime Minister sparked condemnation.
The "sick and offensive" message, sent from the account of Mr Watson, read: "Al Qaeda 1, @David_Cameron 0."
The dig was an apparent jibe at Mr Cameron's decision to postpone his planned trip to Amsterdam for a speech on Europe and instead stay in the UK following the Algerian hostage crisis.
It is believed talks will take place today within the Lib Dem party to determine whether Sir Graham should resign.
Lib Dem leader Nick Clegg "utterly condemned" the tweet.
Sir Graham, who represents the seven county-wide South West, including Cornwall, and Gibraltar, wrote on Twitter: "I wish to apologise profusely for the insensitive tweet I issued earlier. I have taken it down."
This morning, he released a fuller written statement, saying: "I reiterate my profuse apologies for the tweet I issued at 8 pm yesterday. It was ill advised, insensitive and rash and I regret the offence it caused.
"I wrote it at the end of a busy day in Parliament in Strasbourg with no knowledge of how news of the hostage crisis in Algeria had developed throughout the day and unaware that the Foreign Secretary was in Australia.
"In hindsight I recognise that the Prime Minister was absolutely right to postpone his Europe speech in order to deal with a fast deteriorating situation involving the lives of UK citizens.
"I realise it will be of little comfort to the families of those killed or captured but I wish nonetheless to express my sincere condolences to them."
Users of the site called for Sir Graham's resignation over the message, which came as it was reported that two British workers were among the dead following an Algerian military raid to free hostages at a desert gas plant.
A Lib Dem spokesman said the tweet was "sick, offensive and rightly condemned. He's deleted the insensitive comments and profusely apologised".
Alex Folkes, deputy leader of the Lib Dem group on Cornwall Council, said on Twitter: "Dear @GrahamWatsonMEP. There are some times I admire what you do immensely. Tonight is not one of those times."
Conservative blogger and broadcaster Iain Dale said Mr Watson was a "disgrace", adding: "What a disgusting thing to do."
Twitter-user @Biltawulf wrote: "Unelectable insensitive idiot. You just turned people's families into a football score."
The sentiment was echoed by @hughbs, who addressed Mr Watson directly, saying: "Sorry, apology not accepted. You have revealed just how petty and self-serving you really are. Hope electorate will judge."