One of the Royal Marines freed by Iran last week said the group was finding it hard to celebrate in the wake of the deaths of four British soldiers in Iraq.

Corporal Dean Harris said his thoughts were with the families of the four, killed by a roadside bomb near Basra on the day of his release. “It’s so difficult to be ecstatic at a time like this,” he said yesterday.

Prince William was among those mourning for Second Lieutenant Joanna Yorke Dyer, one of those killed, whom the prince described as a “close friend at Sandhurst”. A statement released by Clarence House said: “He [Prince William] is deeply saddened to hear the tragic news . . . He is very much thinking of her family and friends right now.”

Dyer, 24, was an Intelligence Corps officer. The others killed were two 19-year-olds, Private Eleanor Dlugosz and Kingsman Adam Smith, and Corporal Kris O’Neill, 27.

Their deaths are being blamed on Iranian-backed militias using sophisticated technology to blow up the armoured Warrior vehicle carrying the four.

Dyer, an Oxford graduate who passed out of Sandhurst last December, was expected to be a high-flyer in the army. Both her mother and father served and her sister Holly is on leave after serving in Iraq.

Dyer was born in Berlin before the family moved back to Britain. She grew up in a village near Loughborough, Leicestershire. She went to Loughborough high school before studying politics, philosophy and economics at university.

Yesterday the Rev Robin Stapleford, vicar of St Michael’s Church in Hose, where Dyer grew up, said: “The community of Hose is very shocked and saddened and we will remember Joanna in our prayers over Easter. We tend to think of what is going on in Iraq as rather detached, but then something such as this happens and you realise it touches so many people here in the UK. It is very sobering indeed.”

Dyer and her colleagues were returning from a routine patrol in the early hours of Thursday when they were attacked by militias.

British troops have been conducting operations targeting the Shi’ite militias that have received substantial backing from Iran’s Revolutionary Guards.

Intelligence sources said there had been a number of arrests in recent weeks of “individuals who were working to an Iranian agenda”.

British commanders in Basra have accused Iran of paying men as much as £250 a month to attack British troops.

The Warrior is one of the best protected military vehicles in the world but is now vulnerable to Iranian technology, previously used by Hezbollah against Israeli vehicles. Military commanders are reviewing the use of the vehicles.

Read Mick Smith's blog

Times Recommends

• Should Knox’s trial even have reached the courtroom?
• 'Was it real?' The US bailout nightmare
• Iranian opposition plays the long game