The EU's chief negotiator Michel Barnier said that the only way to avoid a no-deal Brexit will be through a majority vote in the House of Commons.
"Over the last days a no-deal scenario has become more likely, but we can still hope to avoid it," Barnier said, adding the EU was ready to accept Britain remaining within the EU's customs union or a relationship similar to the one the EU has with Norway.
He added that a compelling justification would be needed for the EU to agree to a lengthy Brexit delay.
"The UK should now indicate the way forward or indicate a plan," Barnier said. "More today than ever."
UK citizens voted to leave the European Union in a referendum almost three years ago, but the UK parliament has repeatedly rejected the withdrawal agreement, which was presented by the government after months-long talks with Brussels.
The European Union has given the United Kingdom until April 12 to determine alternative withdrawal arrangements, or or exit the bloc without a deal in place on the same date.