Ministers have asked the courts to set aside a landmark ruling that British arms sales to Saudi Arabia are unlawful, a legal manoeuvre that prompted Jeremy Corbyn to accuse the Conservatives of prioritising military exports over civilian lives.

The government has applied for a stay of last month’s judgment pending an appeal, according to Campaign Against Arms Trade, which is fighting the case, at a time when conflict between the Saudis and Houthi rebels in Yemen has intensified.

That appears to contradict assurances given to MPs by Liam Fox, the international trade secretary, that Saudi arms sales would be halted after the ruling pending a review. At the time, 57 export licences were under consideration.

Corbyn said: “This makes a mockery of their own commitment to halt all new sales while a review takes place into civilian casualties. Nothing could be clearer: the government’s priority is to sell arms, not to protect the rights and lives of Yemeni people.”

Thousands of civilians have been killed since the civil war in Yemen began in March 2015. Indiscriminate bombing by a Saudi-led coalition is blamed for about two-thirds of the 11,700 civilian deaths in direct attacks.

At the time of the ruling, Fox told MPs that while the government considered the implications, “we will not grant any new licences for export to Saudi Arabia and its coalition partners which might be used in the conflict in Yemen”.

Andrew Smith of Campaign Against Arms Trade said he believed a stay could be used to allow sales to continue. “The court found that the government acted irrationally and unlawfully in allowing these arms sales. If a stay is granted then it will result in more unlawful arms sales and more atrocities.”

The Department for International Trade said it was not going to grant any new export licences to Saudi Arabia which could be used in Yemen in the light of the court of appeal judgment, although existing export licences are unaffected. But a spokesman added it was seeking to overturn the ruling: “We disagree with the judgment and will be seeking permission to appeal.”

British arms that could be used in Yemen by the Saudis have to be signed off by the foreign secretary and the international trade secretary before a licence can be granted. Since the war began, the UK has sold at least £4.7bn-worth of arms to Riyadh.

Last month’s judgment by the court of appeal held that the foreign secretary, Jeremy Hunt, his predecessor and leadership rival Boris Johnson, and Fox had illegally signed off on Saudi arms exports because they failed to properly assess the risk to Yemeni civilians.

Three judges held that ministers had “made no concluded assessments of whether the Saudi-led coalition had committed violations of international humanitarian law in the past, during the Yemen conflict, and made no attempt to do so”.

Last month, it emerged that Johnson had recommended that the UK allow Saudi Arabia to buy bomb parts expected to be deployed in Yemen in 2016, days after an airstrike on a potato factory had killed 14 people.

Lawyers for the government have asked the court of appeal for leave to take the case to the supreme court and to set aside the existing judgment until the appeal process is exhausted.

On Friday, Corbyn and the Westminster leaders of four other parties – the SNP’s Ian Blackford, the Lib Dems’ Vince Cable, Liz Saville Roberts of Plaid Cymru and Caroline Lucas from the Greens – called on Hunt and Johnson to hold a parliamentary or public inquiry into how the arms sales have been allowed to continue.

There are signs that some involved in the Yemen conflict are eager to escape a conflict that has become a quagmire, described by the UN as causing the world’s worst humanitarian crisis. In the past days, it emerged that a key Saudi ally, the UAE, has quietly begun pulling out its forces as western opposition grows.