Former Norwegian premier Jens Stoltenberg has been named the next NATO chief, stepping in to take over from current secretary general Anders Fogh Rasmussen at a key moment in Europe.

"Mr Stoltenberg will assume his functions as Secretary General as from 1 October 2014, when Mr Fogh Rasmussen's term expires after five years and two months at the helm of the Alliance," NATO said in a statement.

Mr Stoltenberg takes the helm of the 28-nation transatlantic alliance as Europe worries over a Russian build-up on its eastern fringe after the takeover of Crimea.

The 55-year-old was the only candidate for the job.

"I've known Jens Stoltenberg for many years and I know he's the right man to build on NATO's record of strength & success," Mr Rasmussen, who hails from nearby Denmark, said on Twitter.

In almost a decade leading the government, Mr Stoltenberg, who is the head of Norway's Labour Party, became known as a consensus maker, giving him some of the right credentials to maintain good relations with Russia.

Though he never had any particular fondness for defence or security matters, his time as premier of various governments left him with a strong international network and honed his skills as a cross-border negotiator.

The son of a former defence and foreign minister, Mr Stoltenberg negotiated a deal with Russia that ended a four-decade dispute over their Arctic maritime borders and built a personal friendship with then-president Dmitry Medvedev.
He has made it clear that the annexation of Crimea by Vladimir Putin's Russia, which has raised the need for NATO to boost its presence on Europe's eastern edge, cannot stand.
"Russia's use of military force to modify its borders isunacceptable," Mr Stoltenberg said.

"The conflict in Ukraine must be a political solution ... We will not live in a world where the strongest one prevails.
"Russia's move is in breach of international law and it's a type of power policy that belongs in a past era."
Mr Stoltenberg, who lived several years as a child in Belgrade where he learned to speak Serbian, served 22 years in parliament and was prime minister from 2005 to 2013.
"His strength is that he's got a vast political network and good political intuition ... and he will also listen to civil society, not just people within the 'security cage'," said Jan Egeland, a former UN Under-Secretary General.

"If the task for NATO now is to defuse the crisis with Russia over Ukraine, then Stoltenberg will be eminent.

"He thrives on compromise. If the task is escalation, he won't be bad, but there are others who could do a better job," said Frank Aarebrot, professor of comparative politics at the University of Bergen and an acquaintance of Mr Stoltenberg.
"He has a strong presence, in the Bill Clinton sort of way. When he's talking to you, you feel like the most important person in the world."