Sen. Amy Klobuchar met with Ukrainian President Volodymyr Zelenskyy. She received the Order of Merit, First Class. (U.S. Embassy/Klobuchar office/The Minnesota Star Tribune)

U.S. Sen. Amy Klobuchar visited Ukraine on Tuesday for the first time since Russia invaded the country and galvanized many Americans against the aggressor.

"The world's democracies are on the line if Vladimir Putin is allowed to go in and invade and take the territory of a sovereign country," the Minnesota Democrat said during a phone interview from Kyiv. "He will just continue to do it. And the world has to stand up to him. In the face of his unprovoked barbarism, we have to continue to support the Ukrainian people."

Minnesota's senior senator was joined on the trip by Republican Sen. Rob Portman of Ohio. The bipartisan stop included what Klobuchar described as an "incredibly positive" in-person meeting lasting more than an hour with Ukrainian President Volodymyr Zelenskyy. Klobuchar noted that in general "the Ukrainians' morale is strong."

"I come away from this knowing that the Ukrainian people are 100 percent committed to protecting their homeland," she said of the trip. "They will not be beaten down by Putin's evil and that President Zelenskyy is as strong as ever."

Klobuchar and Portman were awarded the Order of Merit, First Class from Zelenskyy during their trip, described as an honor given for "building a sovereign state, active peacekeeping and charitable activity or achievements in economics, science, culture, military or politics."

"Our trip to Kyiv not only offered the opportunity to witness the steadfast resolve of the people but also the leadership of President Zelenskyy and his team," Portman said in a statement. "Now more than ever the United States must stand with our ally Ukraine to send the message to Russia and the world that we will not stand by while sovereign countries are invaded."

Klobuchar visited Ukraine in January with a bipartisan group of senators at a time of rising tension with Russia. The Putin-led country went on to invade in February, scrambling international affairs and bringing a major challenge to the forefront of Democrat Joe Biden's presidency. Congress and the Biden administration have focused on helping Ukraine in the months since the invasion began. Klobuchar also traveled to Poland in March with a bipartisan group of senators and met with military leaders and Ukrainian refugees.

During her trip this week, Klobuchar met Monday with the U.S. Army's 101st Airborne Division in Poland.

"The 101st basically backed up everything that we thought and heard in Ukraine, and that is that the Ukrainians are making very good use of the weapons that we've supplied," Klobuchar said.

While the senator traveled to Irpin and Hostomel Airport this week, she also spent time in Bucha where she said she "saw the site of the mass grave there." The area was where among the best documented Russian war crimes against civilians took place early in the war.

Ukraine has recently claimed to have destroyed bridges and ammunition depots and pounded command posts in a counteroffensive in the Russian-occupied south, and fears continue over the potential for severe damage to a major nuclear power plant.

The fighting complicates what could be a treacherous trip from Kyiv to that Zaporizhzhia, nuclear power plant, Europe largest, by an inspection team from the U.N.'s atomic energy agency.

The experts may have to pass through areas of active fighting, with no publicly announced cease-fire, to reach the Russian-occupied plant, where shelling has driven fears of a catastrophe.

"This could easily lead to a major catastrophe not just for Ukraine, but for the surrounding countries," Klobuchar said before continuing her trip. "And so that is on everyone's minds right now."

The Associated Press contributed to this report.