European Council President Donald Tusk attends a signing of a new agreement on bilateral cooperation and integration, known as Treaty of Aachen, in Aachen, Germany, January 22, 2019. REUTERS/Wolfgang Rattay

BRUSSELS (Reuters) - The European Union is sticking to the Brexit withdrawal agreement, European Council President Donald Tusk tweeted on Wednesday, in what he said was a message to British Prime Minister Theresa May.

“The Withdrawal Agreement is not open for renegotiation. Yesterday, we found out what the UK doesn’t want. But we still don’t know what the UK does want,” he said.