Kosovo's Serb minority is currently protected by a Nato-led force, K-For
The Spanish government has confirmed it will withdraw most of its 600 troops from Kosovo by the end of this summer.
On a visit to Kosovo last week, Defence Minister Carme Chacon surprised many by saying: "The mission has been completed and it is time to return home."
Nato subsequently criticised Madrid for announcing the withdrawal before it had been discussed with its allies, while the US said it was deeply disappointed.
Spain is one of five EU members which do not recognise Kosovo's independence.
Kosovo unilaterally declared independence from Serbia in 2008, nine years after Nato launched an 11-week military campaign to push Serb forces from the province and protect its ethnic Albanian majority.
The Serb minority and their religious sites are currently protected by a Nato-led force, K-For. Also helping to keep order is the EU's largest ever police and justice mission, Eulex, which deployed in December.
On Sunday, the Spanish defence ministry confirmed that the decision to withdraw its troops from Kosovo was firm and that the bulk of the contingent would return home before the end of the summer.
Carme Chacon's announcement in Kosovo surprised many Nato officials
"The Spanish contingent will return in a staggered and flexible manner, so that most of the troops will have returned within the period announced by the minister," it said in a statement.
The ministry said the chief of defence staff was in direct contact with Nato in order to coordinate the pull-out, and that Ms Chacon would meet Nato Secretary-General Jaap de Hoop Scheffer this week to explain.
The minister's announcement surprised many Nato officials, the US government and senior diplomats, who publicly complained that she had failed to inform them through the proper channels.
"If we want to change K-For, the size and the structure of the mission, we must do so as a result of a decision made within the alliance," Mr De Hoop Scheffer said on Friday.
"And this decision should be made in accordance with instructions given by military officials. The conditions for the withdrawal have not yet been met," he added.
US state department spokesman Robert Wood meanwhile said the US was "deeply disappointed" by the announcement.
When asked if Washington shared the Ms Chacon's assessment that the mission had been completed, Mr Wood said: "Not at all".
Following the criticism, Spanish Prime Minister Jose Luis Rodriguez Zapatero explained that he was withdrawing the troops because security had improved and that their role made little sense with Madrid still refusing to recognise Kosovo's independence.