Saudi Arabia confirmed on Monday it had agreed with the British government to buy 72 Eurofighter Typhoon warplanes at a cost of £4.43bn, part of a contract that defence sources said could exceed £20bn.

The announcement was made in a statement from the official Saudi Press Agency, which said the price of each aircraft – which works out at £61.5m ($122.5m, €88.4m) – was exactly the sum paid by the UK’s Royal Air Force for each Typhoon.

The reference to the unit price reflects Saudi sensitivity to the alleged corruption surrounding a previous order with the UK for Tornados, first signed in 1986 and enlarged in 1993. The UK’s Serious Fraud Office abandoned an investigation into alleged bribery in connection with the arrangements last December, citing national security, but the US Department of Justice has since embarked on its own investigation.

The Saudi agency, quoting an official source at the Ministry of Defence and Aviation, said the agreement, called Project Salam, was signed on September 11 “within the framework of the existing close defence relationship between the two countries”. A statement from the UK Ministry of Defence (MoD) described Saudi Arabia as “an important strategic ally for the United Kingdom in the Middle East”.

BAE’s partners in Eurofighter are EADS, the Franco-German-Spanish aerospace and defence company, and Italy’s Finmeccanica.

An adviser on strategic affairs to the Saudi government said that, unlike the Tornado deal, no middlemen were involved in negotiating the agreement. He said a ministerial committee, to be headed by a respected minister of long standing, would be established to supervise the payments and report to King Abdullah.

Negotiations are continuing for the armaments systems to be carried by the aircraft, which could cost an estimated £5bn. A further contract – estimated by some sources at up to £10bn – for support and maintenance of the Typhoon envisages building a big defence infrastructure in the kingdom. That is expected to include the expansion of air bases and the eventual building of capacity that will allow aircraft components to be manufactured in Saudi Arabia.

The Saudi adviser said further negotiations were envisaged for the upgrading of the existing Tornado aircraft, to achieve what he called “a complete redesign of its fighting capabilities”.

UK officials said 24 of the Typhoons would be supplied from aircraft previously scheduled for delivery to the RAF. The 24 would come from the second of three tranches of the air force’s order for Typhoons. The 24 RAF aircraft would be delivered later and, as a result, the RAF’s existing Tornados would have to be kept in service for longer.

Negotiations for a third tranche – a further 88 warplanes on top of the 144 already ordered – were not scheduled to be completed for 18 months, MoD officials said. There is speculation that the third tranche order might be curtailed, with the UK defence budget under pressure and the UK already involved in the US-led Joint Strike Fighter project.