Defence Secretary Philip Hammond has paid tribute to two British troops killed in Afghanistan, saying what happened remains unclear.
He said it was possible that Corporal Channing Day, who served with the 3 Medical Regiment, and Corporal David O'Connor, of 40 Commando, who died on Wednesday, were shot in a "green-on-blue" attack, but investigations are still ongoing.
Mr Hammond spoke on a visit to HMS Bulwark, currently in the Mediterranean, where he joined his French counterpart to watch the first major naval exercise of a combined UK-French force involving 3,000 Royal Navy sailors and Royal Marines.
The Defence Secretary said the drawdown of troops in Afghanistan will still continue as planned and people should be clear of the aims in the country.
"It is a terribly sad loss that we suffered in Afghanistan, our thoughts are with the families and friends of the two soldiers who died," he said.
"It was a tragic incident, the details of which are not yet entirely clear.
"There is an ongoing investigation to establish exactly what did happen but of course the end result is two of our brave soldiers dead, and our thoughts are with the families and friends in what is obviously a very difficult time for them."
But asked whether the latest deaths would speed up the drawdown process, he said: "We are pulling out of Afghanistan. We have a plan to end our combat role by the end of 2014, to draw down significantly during the course of next year but on the way to continue our task of training, mentoring the Afghans so that they can take over the security role.
"Overall the security picture across Afghanistan is steadily improving, I am confident about that, but this is not suburban England and it never will be."
He said people should not lose sight of the "huge gains" and said many people living in Afghanistan could now live in "relative peace, relative calm".