According to Ischinger, the ultimate goal should be a comprehensive peace process under the auspices of the OSCE and the achievement of a political compromise.

"But as long as the situation on the ground tilts in Russia’s favor, a diplomatic solution will be ever less likely," Ischinger wrote.

"Our message should be that if Russia ignores its commitment to help implement the Minsk Protocol, we may have no choice but to provide Kyiv with defense equipment. That would put the ball back where it belongs: in Moscow," Ischinger wrote.

According to Ischinger, ending the violence in Ukraine requires new thinking.

"Those who flatly refuse to consider the difficult options should be aware that inaction also carries responsibility," he said.

"If we do nothing we may well find out that there can and will be a military solution to the crisis over Ukraine," Ischinger said.

Earlier, Ukrainian President Petro Poroshenko called on NATO states to send weapons to his country for the protection and defense against Russian aggression.