A Foreign Office minister has refused to say that Russia has broken international law in Aleppo – despite stating it has killed 3,000 civilians.

Sir Alan Duncan described the controversy as a “technicality”, adding that Russia’s involvement in the war in Syria “does not come across my desk”.

The comments prompted incredulity from a senior Conservative MP, who said the Foreign Office had previously indicated it had no doubt that international law had been breached.

Only last week, Foreign Secretary Boris Johnson – Sir Alan’s boss – accused Russia and Iran of failing to uphold “humanitarian law” in Aleppo.

As the evacuations got underway, Mr Johnson summoned both countries’ ambassadors to criticise their failure to help aid get to the city when it was under siege.

Giving evidence to the Commons Foreign Affairs Select Committee, on "the UK's relations with Russia", Sir Alan said 3,000 civilians had been “killed by Russian activity”.

He also set out how Vladimir Putin’s forces had “destroyed medical facilities” and left “half a million people under siege”, adding: “Nothing really can get more severe than that.”

But, asked if Russia had “violated international law”, Sir Alan replied: “I’m not versed in the detailed technicality,”, adding: “I don’t want to say something that’s inaccurate.”

Mike Gapes, a Labour MP, then said: “You said the Russians have killed 3,000 civilians in Aleppo. If that is the case, have they breached international humanitarian law?”

But Sir Alan replied: “I can’t give you a direct answer on that. I don’t directly cover the Syrian brief.”

The minister said Britain was collecting evidence in Aleppo and “very strongly supporting” an inquiry by the International Criminal Court (ICC).

However, asked if Russia had “committed war crimes”, Sir Alan said: “I can only give the same answer, because I don’t handle the Syrian brief personally.”

He said: “This a very, very technical legal matter’” adding: “That does not come across my desk.”

An astonished Crispin Blunt, the committee’s Tory chairman, said Mr Johnson had clearly implied Russia was “in violation in the way they are conducting this”.

The Foreign Secretary spoke out last week, as the first convoys of evacuees rumbled out of the ruins of Aleppo.

He told MPs: “Both Russia and Iran have failed to uphold their obligations under international humanitarian law, specifically by failing to facilitate the delivery of humanitarian aid to civilians during the months when eastern Aleppo was besieged.”

During the evidence session, Sir Alan described the murder of Andrei Karlov, Russia's ambassador to Turkey, as a “heinous attack”.

He said the Foreign Office had been in contact with the authorities in Turkey and Russia following the assassination on Tuesday.

Sir Alan said: “We obviously fully condemn this, it's a heinous attack.