Spain became the latest country Tuesday to join the US-led coalition striking military targets in Libya, but how the operation will be coordinated when the US pulls back remained mired in uncertainty as NATO members haggled among themselves.

The Spanish parliament approved Prime Minister Jose Luis Rodriguez Zapatero''s request 336-3, with one deputy abstaining. The country is contributing four F-18 fighter jets, a Boeing 707 refueling plane, a submarine, a frigate and a maritime surveillance plane. As many as 500 Spanish soldiers will take part in the operation.

But divisions over whether to have NATO, the north Atlantic military alliance, coordinate the military operation appeared to widen Tuesday. Officials in some countries said they would not participate without NATO, though others have said the alliance''s standing is poor in the Muslim world because of its involvement in the war in Afghanistan.

Sweden, though not a NATO member, is awaiting a solution to the coordination issue before deciding whether to participate in the mission.

"I find it hard to see that any realistic alternative exists to using NATO''s different systems," Sweden''s Foreign Minister Carl Bildt wrote on his blog. He said a level of political leadership that included the participating nations could be placed over NATO''s command structure.

NATO members, meeting Tuesday in Brussels, agreed to have the alliance use sea power to enforce a UN arms embargo on Libya.

But organizations members continued to debate the much more difficult issue of whether the alliance would coordinate enforcement of a UN imposed no-fly zone over Libya.

Besides Spain, countries participating in the operation include the US, Britain, France, Canada, Italy, Belgium and Qatar.