"It is an important task in your land to ensure the reform process is successful," Gabriel told a group of parliamentarians in the capital of Kyiv, DW reported.

"The strongest weapon of democracy is not the military; rather it is to show that people in democracies live better than those in countries without it," he said.

Children must have a bright future, pensioners must be secure and infrastructure built, he said. "That is the biggest danger to foreign aggressors, that the country is well-developed," Gabriel said.

Germans want to help Ukraine, but Gabriel said they also want to ensure that money reaches the people and isn't frittered away through corruption.

Read alsoProsecutors' raid on ex-head of State Affairs Department reveals EUR 1 mln, goldUkraine has struggled to pass a series of structural reforms and tackle corruption, prompting the International Monetary Fund to delay payments of a $17.5 billion (EUR 16.6 billion) rescue package.

The slow pace of reform and continued corruption have hampered the war effort and undermined efforts to accelerate the political process to end nearly three years of conflict with Russia-backed separatists that has claimed some 10,000 lives and displaced tens of thousands.

Gabriel said it was important to first ensure a sustainable ceasefire in the east and the withdrawal of heavy weapons from the contact line as agreed under the Minsk agreements.

Read alsoUkraine reports over 60 attacks on Friday, one soldier wounded"Then the moment will arrive, when one can create the hope for a political process," Gabriel said. "We know who the aggressor is. We know who broke international law. And we know it isn't only about the conflict in Ukraine," he said, hinting at Russia's broader geopolitical goals.

Gabriel's visit came as Ukrainian authorities announced that the head of the country's tax and customs service was suspected in a graft case that cost the state $75 million (EUR 71 million).

The National Anti-corruption Bureau said Roman Nasirov was suspected of "abuse of office, which resulted in grievous harm" to the state. He has been removed from his position as tax boss as an investigation continues.

Investigators believe Nasirov helped parliamentarian Oleksandr Onyshchenko by restricting taxes on gas extraction companies. Onyshchenko is currently on the run.

Masked anti-graft agents gave Nasirov the official notice naming him as a suspect at a hospital where he has been after claiming heart complications, the same day his office was raided.

"I, like many Ukrainian citizens, have doubts about the unexpected transfer to hospital, as this has become a historic tradition for the Ukrainian political elite and top management," anti-corruption prosecutor Nazar Kholodnytsky said.

If convicted, Nasirov would be the first high level official to be prosecuted for graft since the 2014 pro-Western uprising that toppled former President Viktor Yanukovych.