US President Joe Biden is seeking to reinforce Western unity at a series of summits in Europe this week where new sanctions will be announced against Russia over its military offensive in Ukraine, a top US official said on March 22.

Biden left on March 23 for Brussels a day ahead of summits with NATO and the European Council, then a trip to Poland on March 25 for a meeting with President Andrzej Duda the following day.

The intense diplomacy marks a crucial moment in the dangerous standoff between a newly reinvigorated transatlantic alliance and President Vladimir Putin, who a month ago sent the Russian army pouring into pro-Western Ukraine to try and upend the balance of European power.

White House National Security Adviser Jake Sullivan told reporters that Biden will seek to “reinforce the incredible unity we built with allies and partners.”

He also said that unprecedented economic sanctions aimed at crippling Russia’s finances would be deepened.

A further package will be “rolled out in conjunction with our allies on March 24,” Sullivan said. He gave no details, other than to say the package “will focus not just on adding new sanctions but on ensuring that there is joint effort to crack down on evasion on sanctions.”

Another big topic looming for the Western alliance is how to manage China, the world’s second-biggest economy and a partner of Russia.

Beijing has refused to condemn Russia’s military action or support Western sanctions. So far, Washington’s main goal has been to ensure the Chinese do not actively intervene on the Kremlin’s side, either by bailing out the Russian economy or even sending weapons.

Sullivan said there was no sign that China was providing military assistance in the wake of a nearly two-hour phone call between President Xi Jinping and Biden on March 18.

“This is something we are monitoring closely,” he said.

“The president will certainly consult on the question of China’s potential participation in the conflict of Ukraine while he’s in Brussels. He’ll do so at NATO,” Sullivan said.

“He’ll also do so when he addresses the 27 leaders of the EU, because on April 1st, the EU is having a summit with China,” he added.

“We believe we’re very much on the same page with our European partners.”

Although Western-armed Ukrainian forces are “successfully” resisting much of the Russian onslaught, Sullivan warned against any presumption of a quick end to the war or a climbdown by Moscow.

“There will be hard days ahead in Ukraine, hardest for the Ukrainian troops on the frontlines and the civilians under Russian bombardment,” he said. “This war will not end easily or rapidly.”

In a wrinkle for Biden’s travel plans, his chief spokeswoman, Jen Psaki, will have to stay home because of a positive Covid-19 test announced on March 22.

The White House press secretary said she had held two socially-distanced meetings with Biden, who is vaccinated, a day earlier.

However, “the president tested negative today via PCR test,” Psaki said in a statement, adding that Biden, 79, is “not considered a close contact” as defined by the top US health agency.