Five service personnel have been killed in a UK helicopter crash in southern Afghanistan, but the MoD could not confirm the nationalities of the deceased.
Sky News reported the five were all British but the government said it would "inappropriate to comment further until families are informed".
The process of contacting next of kin is ongoing and is expected to last hours, sources said.
If British casualties are confirmed, they would follow the previous deaths of 448 members of UK service personnel in Afghanistan.
The crash makes this the bloodiest day for foreign troops in Afghanistan in 2014.
It brings the total number of international troops killed in the war-torn country this month to seven.
Taliban spokesman Qari Yousaf said the helicopter was on a routine military exercise when Taliban fighters hit it in the Takhta Pul district of Kandahar, Channel 4 News reported.
The helicopter involved is likely to have been a Westland Lynx Mk 9, according to reports.
Lynx helicopters are light utility aircraft used for a wide range of operational capabilities, including transport and resupply.
They usually carry a crew of three, including a pilot, co-pilot and gunner.
It is thought that the other two military personnel on board could have been travelling as passengers.
Defence analyst Paul Beaver said: "It is difficult to speculate on what has happened, but it sounds like this was a flying accident instead of a case of the aircraft being shot down.
"It could be weather related, it could be dust or it could have been trying to avoid birds, for example, or it could be some kind of mechanical failure. There is a whole range of possible causes."
Beaver said that a board of inquiry would have been set up immediately by the Military Aviation Authority to establish the reasons for the crash.
Nato forces are currently preparing to withdraw combat troops by the end of this year, with responsibility for fighting the Taliban insurgency handed over to the Afghan army and police.
The International Security Assistance Force (ISAF) coalition of international forces said earlier today in a statement: "Five International Security Assistance Force service members died as a result of a helicopter crash in southern Afghanistan today.
"ISAF is still in the process of reviewing the circumstances to determine more facts. Our thoughts and prayers go out to the family and friends affected by this tragic event."
A spokesman for Governor of Kandahar province, Tooryalai Wesa, said the accident happened near Kandahar City due to "technical problems", the Daily Mirror reported.
Spokesman Dawakhan Minapal said: "Today at 11am (0630 GMT) an ISAF helicopter crashed due to technical problems in Takhta Pul district. As a result five ISAF soldiers were killed."Suggest a correction