Senator John McCain says the US should oppose Russia.

Reuters Republican Senator John McCain said on Sunday that the United States can only improve its relations with Russia if it adopts a tough stance against President Putin, calling for stronger sanctions against Moscow.

On a trip through the Baltic countries of Ukraine and Georgia, McCain and other senators assured the countries, formerly dominated by the Soviet Union, that the U.S. would support them, despite the praise of the new U.S. president, Donald Trump, for Putin and his criticism of the North Atlantic Treaty Organization (NATO).

"We will strongly encourage our colleagues to impose stronger and more significant sanctions against Russia because of its attack against the United States of America," McCain told reporters in the Georgian capital, Tbilisi.

"I believe that we must continue to improve our relations and understand that Vladimir Putin—unless we confront him—will continue his aggression, and we must oppose Vladimir Putin," McCain said.

On Thursday, US President Barack Obama ordered the expulsion of 35 Russian diplomats and imposed sanctions on two of the country's intelligence agencies over accusations of hacking attacks against US political groups during the elections.

Earlier in Kyiv, McCain pledged continued US support for Ukraine.

"I send a message to the American people that we are with you—your battle is our battle, and we will win together," McCain reportedly said, according to the press office of Ukrainian President Poroshenko.

"In 2017 we will defeat the invaders and send them back to where they came from. Vladimir Putin, you will never defeat the Ukrainian people and deprive them of their independence and freedom," McCain said.

(By Robin Pomeroy)