Herbert Smith, Lovells and Maples Teesdale have all taken lead roles on the sale of the Grade II listed US Embassy building on Grosvenor Square.

The Qatari Diar Real Estate Investment Company – which is owned by Qatar's sovereign wealth fund – has purchased the building in London's Mayfair, with the deal expected to be completed in 2013.

Herbert Smith was instructed by the buyer with a team headed up by real estate partner Don Rowlands with support from real estate associate David Rosen.

Lovells also advised Qatar Diar on the acquisition with commercial real estate partner Francis Giacon leading the firm's team alongside real estate partner Dan Norris.

Maples Teesdale advised the US Government on the acquisition, with property partners Mark Bryan and Neil Sagoo at the helm.

The Mayfair building, built in the 1950s, will operate as an embassy until 2016-17 when the new south London-based US Embassy is expected to be completed.

In a separate deal, Norton Rose and Clifford Chance (CC) have advised Qatar Islamic Bank (QIB) on a $1.1bn (£660m) loan facility for Qatar Diar as it looks to expand its investment portfolio.

Norton Rose banking partner Lucy Wolley Dod advised QIB and syndicated banks while CC was instructed by Qatar Diar, with Dubai-based project finance partner Robin Abraham advising.