Completion of NATO's new $1.2-billion headquarters in Brussels, expected to open this year, has been held up by problems with its IT and communications systems, Belgium said on Monday.

NATO chief Jens Stoltenberg has said he hopes the building will be ready for a summit in 2017, the first for incoming US president Donald Trump, who has expressed reservations over the alliance's role.

Security, especially after allegations of Russian cyber attacks and hacking during the US presidential campaign, is a top priority for the US-led NATO alliance, with its glass and steel HQ near Brussels airport meant to be state of the art.

Asked about reports of hold-ups, a Belgian defence ministry spokeswoman told AFP there "was a bit of a delay (due to problems linked) to information and communication technologies."

The spokeswoman said that while Belgium, as host country, was responsible for overall construction of the building, the information systems had been contracted out separately by NATO.

Asked how long the delay may be, she said she could not say if the work would be completed in the first half of the year, as had been expected, and added that the Belgian government would shortly contact NATO to discuss the problem.

Separately, a NATO official insisted work was in its "final phase", with the building's construction and installation of equipment expected to be largely completed during the coming weeks.

The original plan was for NATO to move into the new HQ this year, "and this plan stands," the official said.

Stoltenberg and other NATO officials have repeatedly warned of the dangers posed by cyber warfare to modern societies dependent on computer and communications networks.