The boss of Irish low-cost airline Ryanair has attacked the UK government-backed rescue of regional airline Flybe, joining industry heavyweight Willie Walsh in opposing state help for a private company.

Ryanair CEO Michael O'Leary said on Thursday he had written to finance minister Sajid Javid, calling on him to extend the same benefits to his airline as it has given to Flybe.

Flybe was kept afloat on Tuesday after its shareholders agreed to invest more money alongside a UK government support plan, but details of that support have not been made public. Media reports say it involves the deferral of a passenger tax (APD) bill and a potential government loan.

The British government has defended the rescue deal and said it is fully compliant with state aid rules.

Walsh, the head of the parent company of British Airways, has complained about the rescue and filed a complaint with the EU saying that help for Flybe constituted a breach of state aid rules.

O'Leary said Flybe should not be singled out for help.

"This government bailout of the billionaire-owned Flybe is in breach of both competition and state aid laws," he said in a statement, adding that any holiday Flybe had been given from APD should be extended across the industry.

Flybe is owned by Connect Airways, a consortium created by Virgin Atlantic, Stobart Group and investment adviser Cyrus Capital.