ZAGREB (Reuters) - Croatia and Serbia vowed on Monday to intensify work on minority rights, border issues and searches for missing persons from their 1990s war, in an effort to improve ties that remain sour decades after the collapse of Yugoslavia.

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Serbian President Aleksandar Vucic and Croatian President Kolinda Grabar-Kitarovic held talk at the beginning of a two-day official visit by Vicic to Croatia.

“The relations between Serbia and Croatia are burdened with the past, which this time we have not talked about... It is our task to talk and seek solutions for issues which divide us,” Grabar-Kitarovic said after the two-hour talks.

Serbia and Croatia are the two biggest republics to emerge from Yugoslavia, which collapsed in 1991. They have sought to improve ties since a 1991-1995 war, but difficulties remain.

To join the European Union, Serbia must resolve outstanding issues with its neighbors, including Croatia.

The two presidents said they had agreed to improve cooperation in the ongoing search for several thousand missing Croats and Serbs from the 1991-95 war.

They also said the two former foes would try to resolve border issues in the next two years. If they cannot, they would turn to an international court.

“We will try to change the atmosphere in the next 100 days, and all the Serbian officials will have to do everything possible for better mutual relations. It will be a signal of goodwill from our side,” Serbian President Vucic said.

“We view the past events differently, but we should mutually understand it, and I think the things will move forward,” he said.

Around 1,000 people gathered to protest on the main Zagreb square against the visit by the Serbian president.

Later on Monday, the two presidents will address a forum of several dozen companies from both countries in an effort to strengthen economic ties. Besides talks with other top officials and the head of the Roman Catholic Church in Croatia, Vucic will visit some areas of Croatia populated by the country’s Serb minority.