EU foreign ministers are concerned that there is insufficient progress on reforms in Ukraine, German Foreign Minister Frank-Walter Steinmeier said on Monday.
"There are shortcomings in the area of justice, especially the fight against corruption," he told journalists in Brussels after talks with his EU counterparts.
The European Union has stood by Ukraine as it has faced a pro-Russian separatism in the east and tensions with Moscow. But ministers also underlined on Monday the necessity for Kiev to uphold its end of a peace deal that has been agreed to with Russia.
"We continually remind [the Ukrainians] of their obligation to comply with their requirements, ... to make sure that they can look the Russians firmly in the eye when denouncing them for not complying," British Foreign Secretary Philip Hammond said.
"If it's possible to make progress in the implementation of the Minsk [peace] agreement on both sides - not only with a real ceasefire, but also with some reforms in Kiev - it will be possible to change the way," Belgian Foreign Minister Didier Reynders added.
He said it was important to see progress in Ukraine on the fight against corruption, judicial reforms and decentralization measures. The EU has made its financial aid to Kiev conditional on reforms.
Steinmeier said they are also key given the economic situation in the country, which is standing on the edge of bankruptcy due to the months-long civil war between government forces and the pro-Russian separatists in the east.
Ukraine will only become attractive again for investors if it offers as corruption-free an environment as possible, Steinmeier argued.
At the same time, he praised Kiev's progress in the area of economic and finance legislation, energy policies and law enforcement.
"We were all united in applauding and encouraging the outstanding work that the Ukrainian authorities have done in the past months in order to introduce and start implementing reforms," EU foreign policy chief Federica Mogherini added.
"I think we've learned from the past ... that once you start a process, that is never enough," she said. "You also need to continue focusing on how you can better make it sustainable."