By MARC CHAMPION

BRUSSELS–The Netherlands has given its foreign minister a green light to begin unblocking Serbia’s path to membership in the European Union, if an upcoming report finds Belgrade is cooperating fully with the war crimes tribunal for ex-Yugoslavia, a Dutch foreign ministry spokeswoman said Thursday.

While the EU has pledged Serbia can eventually join the 27-nation bloc, the Netherlands has prevented a key Stabilization and Association Agreement with Belgrade from taking effect.

Such agreements are considered a necessary first step before membership talks can begin.

Late Wednesday, the main parties in the Dutch parliament gave foreign minister Maxime Verhagen approval to “act accordingly” if a report due Dec. 3 from Serge Brammertz, chief prosecutor of the International Criminal Tribunal for the former Yugoslavia, shows that Serbia is now cooperating fully with the tribunal, the spokeswoman said.

The decision was the clearest signal to date that the Netherlands may be ready to approve the deal. Dutch governments have taken a hard line on pressuring Serbia to come to terms with its role in the 1992-1995 war in Bosnia, in part because of the humiliation of Dutch peacekeepers protecting the United Nations safe haven of Srebrenica in 1995.

Bosnian Serb troops led by Gen. Ratko Mladic overran the territory, as the Dutch peacekeepers looked on helplessly. Some 8,000 Bosnian Muslim men and boys are believed to have been executed in the aftermath.

Last year, a newly elected pro-Western government in Belgrade captured war-time Bosnian Serb leader Radovan Karadzic and delivered him to the tribunal in The Hague.

But with Gen. Mladic and one other Serb indictee still in hiding, Holland has continued to block Serbia’s stabilization agreement.

No-one in the Dutch government has seen a draft of Mr. Brammertz’s report, but Mr. Verhagen told parliament Wednesday that “the first signals are positive,” according to the foreign ministry spokeswoman. Holland’s tough line on Serbia has created tensions within the EU. Many governments worry the bloc needs to keep Serbia on track for membership to maintain stability in the region.

The EU supported Kosovo’s secession from Serbia last year and is trying to manage the fallout from that, as well as an increasingly unstable situation in Bosnia. The EU is also expected later this month to begin consideration of a request from Serbia’s regional rival Albania to start membership talks. The Netherlands has already begun to soften its position against Belgrade, saying it won’t stand in the way of granting Serbs visa free travel to the EU, expected next year.

Last week, Serbia’s government said it also plans to apply for EU membership talks by the end of the year, a move that Italy has since backed publically. The Netherlands would oppose such an early move, however, the foreign ministry spokeswoman said, arguing that Serbia should not skip the association agreement.

Separately Thursday, an appeals bench at the war crimes tribunal cut the sentence of a Bosnian Serb found guilty of war general from 33 to 29 years.

The court upheld Dragomir Milosevic’s convictions on five counts of murder and other crimes while leading troops who besieged Sarajevo.

Write to Marc Champion at marc.champion@wsj.com