Nato is building a new, state-of-the-art headquarters in Brussels, but critics say the $1 billion project seems extravagant at a time when austerity is forcing many alliance members to slash military spending.

The vast steel-and-glass structure is taking shape in the outskirts of Brussels, across the road from the old headquarters, built as a temporary home for the alliance in 1967 and which Nato officials say has outlived its useful life.

Construction is 80 percent complete on the new building, made up of eight curving wings that connect to a huge central space with an imposing 32 metre (yard)-high entrance.

More than 4,000 Nato staff and diplomats from the 28 allies and 22 partner countries are to move in 2016.

Nato members have shared the cost of the new headquarters at a time when many are being forced to cut key military capabilities due to a budget squeeze.

Nato also faces questions about its future after it ends combat operations in Afghanistan at the end of next year.

"When defence budgets are being cut and in general when governments are under so much pressure from taxpayers to save money, it looks terribly extravagant," said Daniel Keohane, head of strategic affairs at the Fride think tank in Brussels.

Nato leaders gave the go-ahead for a new headquarters in 1999, long before the financial crisis broke. But the timing of the construction of the eight-floor structure, including enough blast-resistant glass to cover 10 football pitches, was "unfortunate", Keohane said.

Several British legislators have been quoted in the media as questioning the cost.

21ST CENTURY

Matthew Klimow, a Nato deputy assistant secretary-general, said the new headquarters was "far from extravagant".

"It is a functional building that will allow us to say to the world that Nato is ready for 21st-century challenges," he told Reuters during a media tour of the new headquarters.

Klimow said the current Nato headquarters was designed to last for only 10 years when it opened in 1967. Portable buildings were installed to house extra staff as the alliance grew from 15 nations in 1967 to 28 today.

Electrical systems are archaic, concrete floors crumbling and the grounds teeming with stray cats and rabbits which burrow under the foundations, officials say.

The new headquarters will be environmentally friendly and have advanced communications and security, they say. It is being built near the site of a World War Two German airfield and construction was delayed for months after two unexploded bombs were found. - Reuters