BELGRADE, Serbia (AP) — Serbia and Croatia each have expelled a diplomat from the other country, a move that further strains relations between the two former wartime foes and Balkan rivals.

The Serbian Foreign Affairs Ministry said Monday that the first secretary of the Croatian Embassy in Belgrade was proclaimed persona non grata for his alleged “gross stepping outside the framework of diplomatic norms” during his service.

In a reciprocal move, Croatia expelled a Serbian diplomat on Tuesday.

“We have decided that the adviser of the Embassy of Serbia in Croatia, Petar Novakovic, should be declared persona non grata in Croatia,” Croatia’s Foreign Minister Gordan Grlic Radman said.

Media close to the populist Serbian government said the Croatian diplomat, identified as Hrvoje Snajder, is accused of “spying activities” and “recruiting” of people for Croatian secret services.

The Croatian Ministry of Foreign and European Affairs rejected the grounds for the diplomat’s expulsion and called Serbia’s action “a step toward the deterioration of mutual relations” at a time “when the stability of southeastern Europe is of exceptional importance for the whole of Europe.”

Tensions between the two Balkan neighbors have off and on been tense since the Balkan wars in the 1990s when the Serbian-led troops intervened in Croatia in a land grab operation that ended in a defeat of Belgrade and the expulsion of tens of thousands of ethnic Serbs who lived there.