US President Joe Biden said he would lay down "red lines" to Russian counterpart Vladimir Putin at their meeting today in Geneva.
Speaking after his first NATO summit, Biden insisted: "I'm not looking for conflict with Russia, but that we will respond if Russia continues its harmful activities."
The warning came as Biden pressed to renew Washington's transatlantic ties with allies following tensions under Donald Trump.
"Russian-US relations are now at an impasse, the situation is close to critical. Something needs to be done," Yuri Ushakov, Putin's foreign affairs adviser, said. "I view this meeting with practical optimism, but not much. It is a first meeting under difficult circumstances."