U.S. Sen. Cory Gardner has joined a bipartisan effort calling for sweeping new sanctions against Russia.

Gardner, who sits on the Senate Foreign Relations Committee, announced his support for sanctions after meeting with Ukrainian former Prime Minister Yulia Tymoshenko to express U.S. support for Ukraine and to condemn Russian aggression.

“Vladimir Putin’s continued aggression toward our allies in the region, and repeated malicious cyber activity against the United States, needs to be dealt with now,” Gardner said in a statement. “Russia’s behavior must be met with strength in the form of aggressive sanctions to show the world that its actions will not be tolerated.”

Gardner’s statement comes as U.S. ambassador to the United Nations Nikki Haley, in her first appearance at the UN Security Council, called on Moscow to de-escalate violence in eastern Ukraine. She stood firm this week that sanctions against Russia would continue until it withdraws from Crimea. Haley is President Trump’s diplomat to the world.

The UN held an emergency meeting this week to address a sudden uptick in violence in eastern Ukraine, where Russian-supported separatists continue to battle the Ukrainian army. In some ways, Haley departed from Trump on the subject.

Questions continue to circulate over what connection Trump has to Russia, including whether Moscow may have compromising information about the president. Trump has refused to criticize Russia for apparent hacking during the election, and on the campaign trail he even alluded to acknowledging Russia’s takeover of Crimea.

Trump has also been reluctant to rush into directly addressing sanctions on Russia.

Meanwhile, fighting in eastern Ukraine has cornered thousands of civilians and destroyed wide swaths of infrastructure. It appears the confrontation is growing.

The subject is not new to Gardner, who last year co-sponsored a resolution calling on Russia to cease military actions that endanger U.S. forces, and urged European allies to pressure Russia.