Nato leaders are set to commit to a big hike in defence spending and the Secretary General has said there is no alternative.

European allies should not worry about the United States' commitment to NATO, Mark Rutte, the chief of the military alliance, said on Tuesday, speaking before a summit that is likely to sign off a big new spending goal.

At the recent summit in The Hague, NATO Secretary-General Mark Rutte addressed key security challenges facing the Euro-Atlantic region, including the long-term threat posed by Russia and the rapid military expansion of China.