The UAE will finalise an estimated $7 billion deal to buy an advanced missile defence system from Lockheed Martin this spring, the first such export by the US firm, a Lockheed official said on Sunday.

The UAE has been negotiating the acquisition of the Terminal High Altitude Area Defense, or THAAD, since late 2008 when the US defence department announced the proposed sale.

'We are very close to finalising documentation necessary to have a successful programme for the UAE. This spring, the US government will make an announcement,' Dennis Cavin, vice president, International Air & Missile Defence Strategic Initiatives for Lockheed Martin told Reuters at a defence expo.

The deal was negotiated between the US and the UAE governments directly. The United States government is expected to send a letter of agreement in the next few months, the Lockheed official said, after which the UAE could start negotiations with contractors on production schedules.

US defence major Raytheon will support Lockheed in providing logistics and sustainment services.

UAE defence officials declined to comment on the deal. But sources familiar with the matter told Reuters on Sunday the deal was in its final stages and could be sealed soon.

Thaad is a key element of the Ballistic Missile Defence System (BMDS) designed to defend troops, allied forces, population centres and critical infrastructure. The weapon system is fully integrated, comprising five major components - launchers, interceptors, a radar, Thaad fire control and communications and specific support equipment.

In late 2008, the UAE closed a deal with Lockheed Martin to buy advanced Patriot anti-missile systems. The UAE has started receiving the PAC-3, a Lockheed spokeswoman said on Sunday without elaborating.

The International Defence Exhibition & Conference (IDEX), the region's largest military expo, opened on Sunday in Abu Dhabi with some 1060 companies participating.-Reuters