Western Leaders attending a slew of emergency summits Thursday were working to settle on the next phase of their  response to war in Ukraine.

What can they do?

Announcements on new sanctions, NATO force posture and military assistance were all expected as part of the last-minute diplomatic burst, according to US and European officials. US President Joe Biden was expected to unveil a plan to accept as many as 100,000 refugees fleeing the violence.

What they won't do

What they won't do, however, is what UkZelensky has repeatedly asked: Enforce a no-fly zone over Ukraine. US and NATO officials have repeatedly said that such a move would risk provoking Russian President Vladimir Putin and sparking a wider war with Russia. Western allies have also found it difficult to take more aggressive steps, such as providing Russian-made fighter jets to Ukraine or deciding to cut themselves off from Russian energy supplies, which could potentially cripple Russia's economy.

The crisis sessions of NATO, the European Council and the G7 were arranged last-minute, leaving little time for the normal back-and-forth between governments that precedes such events. Biden determined earlier this month that an in-person gathering of a newly united Western alliance would signal resolve to Putin.

Whether Putin views it that way -- or whether cracks are exposed among the allies on sanctions and use of military force -- remains to be seen.

It's a critical moment for Biden, Europe and the world. Harsh coordinated sanctions already imposed by the West have not stopped Putin's invasion, which is entering its second month. Biden warned as he was departing the White House for Brussels that chemical warfare posed a "real threat" in Ukraine. And massive refugee flows are quickly turning into a humanitarian crisis for Ukraine's neighbors.