The diplomatic incident also came hot on the heels of Serbia's change of position on EU membership, after the visit of German Chancellor Angel Merkel, from "both EU and Kosovo" to "Kosovo before EU."
On August 24, Kosor said in Pristina that her country was Kosovo's best friend because both countries suffered from the nationalist and war-making regime of late Serbian leader Slobodan Milosevic in the 1990s.
Serbia's increasingly gaffe-prone and blunt-speaking foreign minister, Vuk Jeremic, blasted her a day later: "Whoever has Jadranka Kosor as a best friend, doesn't need enemies."
On August 26, Kosor said that after 20 years of independence, won after a bloody war with Belgrade-backed Serbian separatists in the early 1990s, no Croatian politician or prime minister would ever again go to Belgrade to ask for permission about what to do or think.
"Those times are, luckily, gone forever," she said.
No More Mr. Nice Guy
This type of rhetoric in Serbian-Croatian relations appeared to be over after the pro-European and mild-mannered Ivo Josipovic was elected president of Croatia in early 2010, replacing Stipe Mesic, who rarely minced words when it came to criticizing Serbia over Kosovo and its support for separatist Bosnian Serbs.
Josipovic and his Serbian counterpart Boris Tadic have held a series of meetings that, despite occasional hiccups related to unresolved war-related issues, appeared to have improved relations in the region.
Serbia has also held EU-sponsored technical talks with Kosovo on administrative and bread-and-butter issues, but these have stalled and appear uncertain after last month's rioting by Kosovo Serbs after Kosovo's police tried to take over border crossings in Serb-held northern areas.
Merkel told Serbia that it had to dismantle parallel structures it supports in northern Kosovo if it wanted to move closer to the EU. Belgrade had hoped to get candidate status by the end of the year.
But with a clear choice on Kosovo to make and Serbian general elections scheduled for spring next year, Tadic has shifted the Serbian policy to the right, saying, "If we are going to get a request for Serbia to make a choice...my answer would be that Serbia would not give on any of its political interests."
Independent parliament deputy Vesna Pesic told RFE/RL: "Starting [with] the [Serbian Orthodox] Church, everybody thinks that Serbia should not betray Kosovo. This means that because of the forthcoming elections and internal pressure from the general public, [Tadic] needs to act tough."
-- Nedim Dervisbegovic, with reporting by Ankica Barbir Mladinovic in Zagreb and Ljudmila Cvetkovic in Belgrade