The European Union has drafted a declaration on behalf of 27 member states in response to the United Kingdom's official exit notification expected Wednesday, a diplomatic source told Sputnik.

UK Prime Minister Theresa May is expected to trigger Article 50 of the EU treaty later in the day, formally launching the Brexit process.

"It is expected that immediately after the official notification of Brexit, a declaration of the leaders of 27 EU countries will be made public," the source said.

European Council President Donald Tusk has said that he would formally respond to the notification and lay out the Brexit strategy within 48 hours of the start of Brexit.

The 27 European Union member states' permanent representatives could gather on Friday to draft a detailed Brexit negotiations plan, the source added.

"A meeting of the EU ambassadors is planned for March 31, which will begin to develop a detailed plan for the upcoming negotiations on Brexit," the EP source said.

The source said the plan would be drafted for consideration at the April 27 European Council meeting and the April 29 Special European Council on Article 50.

The Brexit letter will be delivered by UK's Permanent Representative to the EU Tim Barrow at 12:20 GMT on Wednesday, European Council President Donald Tusk has confirmed.