US President Joe Biden has called on Russian President Vladimir Putin to step back from provocative actions targeting the United States and its allies.
Mr Biden's words for Russia, spoken during his first appearance at a NATO summit, contrasted with his friendly interactions with NATO allies, signifying a clear shift in tone from the past four years.
It also highlights the renewed US commitment to the 30-country alliance that was frequently maligned by his predecessor Donald Trump.
The US president said other leaders were supportive of his plans to press the Russian leader to halt Russian-originated cyber attacks against the West, end the violent stifling of political dissidents and stop interfering in elections outside its borders.
Ending his day at NATO headquarters, Mr Biden said: "I'm going to make clear to President Putin that there are areas where we can co-operate if he chooses.
"And if he chooses not to co-operate and acts in a way that he has in the past relative to cybersecurity and other activities, then we will respond, we will respond in kind."
During his eight-day visit to Europe Mr Biden is seeking to rally allies to speak with a single voice on countering Russia and China.
On Monday, NATO leaders declared China a constant security challenge, implying the Chinese are working to undermine global order, a message backing up Mr Biden's pleas to confront Beijing on China's trade, military and human rights practices.
The leaders said in a summit statement that China's goals and "assertive behaviour present systemic challenges to the rules-based international order and to areas relevant to alliance security".
This led to China describing the comments as "slander" in response.
NATO leaders also addressed Russia's supposedly aggressive military activities and its wargames near the borders of NATO countries as well as the repeated violations of their airspace by Russian planes.
They said that Russia had ramped up "hybrid" actions against member countries by attempting to interfere in elections, by political and economic intimidation, by disinformation campaigns and "malicious cyber activities".
"Until Russia demonstrates compliance with international law and its international obligations and responsibilities, there can be no return to 'business as usual'," they said.
Cover image: US President Joe Biden during the NATO summit in Brussels (Picture: Sipa US/Alamy).