"Despite many difficulties that currently exist in those countries, progress has been made," Merkel said in the video message broadcast on Saturday ahead of her visit to the western Balkans next week.
She was quoted by the dpa news agency as saying that the prospects of EU membership could help western Balkan countries to resolve their differences.
Merkel is due to arrive in Serbia on Wednesday, 8 July. Her visit to Sarajevo is scheduled for 9 July.
The influx of migrants from the region, who seek asylum in Germany, will be on the agenda of the talks, too.