NATO Secretary General Mark Rutte said Friday’s summit between President Donald Trump and Russian President Vladimir Putin in Alaska will be an important test in ending the war in Ukraine.

“Next Friday will be important because it will be about testing Putin, how serious he is on bringing this terrible war to an end,” Rutte told ABC News' “This Week” co-anchor Jonathan Karl.

“It will be, of course, about security guarantees, but also about the absolute need to acknowledge that Ukraine decides on its own future, that Ukraine has to be a sovereign nation, deciding on its own geopolitical future,” Rutte added.

Rutte said he believes that Trump supports these terms as well.

“The president wants to end this. He wants to end the terrible loss of life,” Rutte said.

The NATO chief also acknowledged the reality that Russia is in control of some of Ukraine’s prewar territory.

“The question will be how to go forward past a ceasefire, including what it means in terms of security guarantees for Ukraine,” he said.

This is a developing story. Please check back for updates.