German Chancellor Angela Merkel and European Council President Donald Tusk rebuffed a call from pro-Brexit British MPs for a quick deal on mutual residence rights for British and EU expatriates, telling them on Tuesday it was up to their government to launch full-blown divorce talks. The exchange of letters exposed simmering irritation on both sides of the English Channel before Brexit talks even start.

British Prime Minister Theresa May herself is pushing for "an early resolution" to anxiety facing over 3 million EU citizens in Britain and over a million British expats. But she has faced a phalanx of EU leaders, including German Chancellor Angela Merkel and EU Brexit negotiator Michel Barnier, who rule out any negotiation until she triggers the exit process under Article 50 of the EU treaty.

She has irked her partners by holding off doing so since the June referendum vote to leave, but says she will do it by March.

Triggering talks will set Britain a two-year deadline to cut a deal it hopes can protect its trade with the bloc while ending free immigration from the EU. Without a deal, it faces a sharp and disruptive exit which both sides say they do not want.

Over 80 British parliamentarians from the pro-Brexit European Reform Group wrote to Tusk on Friday asking that the EU summit he will chair on Dec. 15-16 "guarantee ... reciprocal rights" for people living abroad on either side of what will be a new EU-UK frontier once Britain has left the European Union.

It was a "technical and administrative matter" that could be resolved swiftly, they wrote: "No European expatriate's livelihood and family should be held hostage in this way."

Tusk, a former prime minister of Poland whose citizens make up the biggest group of EU expatriates in Britain, said the Council could only address the matter once London opens talks and argued that only a full negotiation could settle the issue.