US authorities have given approval for Lockheed Martin to acquire Sikorsky aircraft from United Technologies for $9bn in cash.

Lockheed expects to close the deal by the end of this year, or early next year.

The agreement has also received permission from authorities in Japan and South Korea, but is awaiting necessary regulatory approvals from the European Union, China and countries where one or both companies have business concerns.

US agencies involved in the review of the deal include the US justice department, Pentagon and other federal agencies.

The acquisition would open key foreign markets for Lockheed, which has annual revenues of $45bn, and already dwarfs its nearest competitors, the defence businesses of Boeing and Northrop Grumman.

"Exiting the helicopter business will allow UTC to better focus on providing high-technology systems and services to the aerospace and building industries."

Lockheed is considering selling or spinning-off $6bn of its information systems and government services business.

The company also plans to merge the Sikorsky acquisition into its mission systems and training operation, to generate about $15bn revenue each year.

Sikorsky is Lockheed’s largest acquisition, after the purchase of Loral Corp’s defence electronics business for $9.1bn in 1996, and the merger with Martin Marietta in 1994 for $10bn.

United Technologies announced the sale of its Black Hawk helicopter-maker Sikorsky to Lockheed in July this year.

United Technologies president and CEO Gregory Hayes said: "We are very pleased to announce this transaction.

"Exiting the helicopter business will allow UTC to better focus on providing high-technology systems and services to the aerospace and building industries, and to deliver improved and sustained value to our customers and shareowners.

"Sikorsky’s acquisition by Lockheed Martin, one of the world’s leading aerospace and defense companies, will ensure it remains a technology leader at the forefront of vertical lift."