EU President Donald Tusk on Saturday urged the bloc to keep a united front at a special Brexit summit in Brussels, saying it will also help Britain if they can reach a deal.
"We need to remain united as the EU 27. It is only then that we will be able to conclude the negotiations, which means that our unity is also in the UK's interest," Tusk told reporters.
"We also need solid guarantees for citizens and their families, who will be affected by Brexit on both sides. This must be number one priority for EU and the UK," he said.
This referred to the fate of three million EU citizens living in Britain and one million Britons on the continent, with officials hoping for a resolution on their status after the divorce by the end of the year.
The call for a united front comes hot on the heels of a war of words between German Chancellor Angela Merkel and British Prime Minister Theresa May over the negotiations.
The EU 27 have considerably toughened the guidelines since Tusk first unveiled them in March, shortly after May triggered the two-year Brexit process.