The United States sent a letter to Russia addressing the country’s security demands, but did not make any concessions, Secretary of State Antony Blinken said Wednesday.

The missive is “a serious diplomatic path forward,” Blinken said, and is the latest attempt to cool tensions between Russia and Ukraine. The letter’s contents won’t be made public, Blinken added, but he did say it mentions Russia’s demand that Ukraine be barred from joining NATO. “NATO’s door is open, remains open, and that is our commitment,” Blinken said. 

President Biden was “intimately involved” in writing the letter, Blinken shared, and it is made clear in the message that the Biden administration is dedicated to helping Ukraine keep its sovereignty and “the right of states to choose their own security arrangements and alliances.” 

The letter does not contain “explicit proposals” and isn’t “a formal negotiations document,” Blinken said. “The ball is in their court,” he added. “It remains up to Russia how to decide to respond. We’re ready either way.”

In addition to permanently banning Ukraine from NATO, Russia wants a roll back of NATO military deployments in Eastern Europe. Earlier Wednesday, Moscow said if its security demands are not met, it would take “retaliatory measures.”