The European Union will be more insistent that western Balkan states apply the rule of law than it has been with previous enlargement candidates, the EU enlargement commissioner said on Wednesday. "We have learned from the previous round of enlargement and now with Bulgaria and Romania that, even though the rule of law has been previously included in the ... political criteria before starting negotiations, it often gets left to the last mile," Olli Rehn told Reuters in an interview. "We really need to focus more on the building of (democratic) institutions and administrative capacity in the western Balkans," he said on the sidelines of a South-East European Cooperation Process (SEECP) summit in Bucharest, adding that these countries had more ground to make up. "The rule of law is the most fundamental value of the European Union," he said. Romania and Bulgaria are set to join the EU in 2007 after missing a first eastward enlargement last year -- but have been warned that they will be held back if they fail to fight corruption and crime and reform their court systems. --More 2103 Local Time 1803 GMT