Ukraine faces a “serious moment” in its defence against the Russian invasion, Defence Secretary John Healey said as he refused to be drawn into confirming reports the war-torn nation has launched British-supplied long-range missiles at its foe.

Russia’s military said it has shot down two British-made Storm Shadow missiles, following reports that debris from the weapons had been discovered in the country’s Kursk region, which borders Ukraine.

The Prime Minister has meanwhile insisted UK support for Ukraine is “always for self-defence” and compliant with international law, as he accused Russian President Vladimir Putin of wanting “destruction not peace”.

Kyiv has meanwhile claimed Moscow has fired intercontinental ballistic missiles (ICMBs) at one of its cities, which would be the first time such a weapon has been used in the war.

British ministers have avoided questions about whether the UK has given permission for Volodymyr Zelensky to fire its long range missiles into Russian territory, after President Joe Biden announced the United States had.

And at the first session of the Commons Defence Committee this Parliament, Mr Healey proved no exception.

Asked to confirm reports Storm Shadow had been used by Ukraine, the Defence Secretary said: “I won’t be drawn on the operational details of the conflict.

“It risks both operational security and in the end the only one that benefits from such a public debate is President Putin.”

Battle lines in Ukraine are now “less stable than at any time since the early days of the full scale Russian invasion”, Mr Healey said, citing British intelligence.

“This is a serious moment that I come before the committee,” he told MPs.

Mr Healey added: “While the Ukrainian actions on the battlefield speak for themselves, be in no doubt that UK Government is stepping up our support for Ukraine, determined to continue doubling down our support for Ukraine.”

Speaking at the same time, Sir Keir Starmer told the House of Commons the UK “will not be deterred or distracted by reckless threats”, in reference to Vladimir Putin lowering the threshold for using his nuclear arsenal.

This was widely seen as a response to Mr Biden’s announcement he would give Ukraine permission to use US-made long-range ATACMS missiles.

Sir Keir also told MPs: “We have consistently said we’ll do what it takes to support Ukraine and put it in the best possible position going into the winter.

“The UK’s support for Ukraine is always for self-defence, it is proportionate, co-ordinated, agile and a response to Russia’s own actions and it is in accordance with international law.”

Downing Street later described the unconfirmed reports Russia had launched an ICBM into Ukraine as “deeply concerning”.

But the Prime Minister’s official spokesman said he did not “want to get ahead of our intelligence services who are looking at these reports urgently”, adding: “But if true, clearly this would be another example of grave, reckless and escalatory behaviour from Russia and only serves to strengthen our resolve.”

On Wednesday, the Defence Secretary announced that two former Royal Navy flagships, a frigate and a pair of support tankers would be decommissioned.

During the committee hearing, Mr Healey said UK military equipment capabilities were in large part “not good enough for the future” and that “our forces deserve better equipment to do their job better”.

Mr Healey told the committee: “The rapidly changing nature of warfare that Ukraine tells us and amplified by the accelerating development of technology means that the sort of capabilities in large part that we have are just not good enough for the future.

“When we work with allies, we have to make sure that our UK contribution isn’t just a major contribution to the collective deterrence and strength of our alliances, but is also part of the leading edge that sees us setting the pace of some of the necessary transformations.”

Mr Healey said the UK was “doing everything that we can” to make sure Ukraine was “successful on the battlefield and capable of withstanding the Russian pressure”.

He added: “If President Zelensky and the Ukrainians decide there is a point, at some point, that they want to start the talking, our job will be to support them in any of the negotiations, just as it is with the fighting.”