UN Security Council member Spain called Thursday for a deal to end unrest in Libya within weeks and said a UN resolution would be needed to approve any NATO intervention there.

Concerned by violence and the rise of Islamist groups in Libya, Spanish Foreign Minister Jose Manuel Garcia-Margallo appeared in Madrid alongside NATO Secretary General Jens Stoltenberg to tout security cooperation in the region.

A NATO air campaign in Libya in 2011 backed the uprising that ousted and killed dictator Moamer Kadhafi. Rival groups are now battling for control of the country's cities and oilfields.

Western powers including Spain, which this year holds a non-permanent seat on the Security Council, have insisted on a political solution but have not definitively ruled out another intervention.

Garcia-Margallo said that if UN-brokered talks led to the creation of a "unity government" in Libya, that body could then "request the support that it considers appropriate in Libya, which is the top item on our agenda".

"Any NATO intervention in Libya, which right now it is too soon to decide upon, would require a UN Security Resolution," Garcia-Margallo told a news conference alongside Stoltenberg.

"Once such a resolution is passed, it will be up to the bodies within the alliance to take the most appropriate decision to achieve stability in Libya, which is an urgent matter," he added.

"We are not talking months, we are talking weeks, to reach a solution," he said, warning that the security situation in Libya "is posing a risk to the stability of a whole region around us".

NATO has announced it will more than double its ground "response force" to 30,000 personnel, including a new 5,000-strong "quick reaction force" known as Spearhead.

Spain will next year be the first country to lead Spearhead when it launches next year, Stoltenberg said.

"That will increase our readiness and then we can deal with threats both from the east and from the south," Stoltenberg said on Thursday, referring respectively to unrest in Ukraine and North Africa.

On eastern Ukraine, where pro-Russian separatists are battling Ukrainian forces, Stoltenberg reiterated his call for a ceasefire to be respected. He called for international observers to be allowed to safely monitor the ceasefire and withdrawal of heavy arms.