Ukraine will need strong armed forces and security guarantees after any peace deal with Russia is agreed to and Kyiv should not be forced to surrender territory, German Chancellor Friedrich Merz said on Thursday.

Stressing that European as well as Ukrainian security interests were at stake, Merz said guarantees were being discussed with the U.S. and Ukraine.

"Ukraine needs strong armed forces, and if a peace agreement is reached ... Ukraine will continue to need strong armed forces and reliable security guarantees from its partners," said Merz at a press conference with his Estonian counterpart.

The most important guarantee, he said, was a well-equipped Ukrainian army.

"That is why we are also discussing the future target size of the Ukrainian army," Merz said, adding it was too early to discuss any deployment of international troops.

European countries have insisted that the upper limit for Ukraine should be 800,000 soldiers rather than 600,000.

Merz also said Ukraine should not be forced to accept territorial concessions and that the front line must be the starting point for any negotiations.