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Theresa May has met European Council President Donald Tusk ahead of the start of Brexit talks and stressed the "positive" tone shown by both sides.

After this week's row about Gibraltar, an EU source said they would "seek to lower tensions that may arise".

Downing St said the PM "made clear" that "there would be no negotiation on the sovereignty of Gibraltar without the consent of its people".

Mrs May formally triggered two years of Brexit talks last week.

A Downing Street spokesman said: "The PM reiterated the UK's desire to ensure a deep and special partnership with the European Union following its exit and noted the constructive approach set out by the council in its draft guidelines published last week."

"Both leaders agreed that the tone of discussions had been positive on both sides, and agreed that they would seek to remain in close touch as the negotiations progressed.

He added that Mrs May had made clear "the UK would seek the best possible deal for Gibraltar as the UK exits the EU".

Downing Street said they had also discussed the agenda for the next EU Council meeting as the UK remained a "full and engaged member" of the EU.

Mr Tusk has warned the Brexit negotiations could become "confrontational" at times.

Leaving the talks, Mr Tusk had simply said "no", when asked a series of questions including whether Gibraltar had been discussed and what the tone of the talks had been. Asked if the talks had been successful he replied: "As always."

An EU source said Mr Tusk and Mrs May had a "good and friendly" meeting of about two hours: "They agreed to stay in regular contact throughout the Brexit process to keep a constructive approach and seek to lower tensions that may arise, also when talks on some issues like Gibraltar inevitably will become difficult,"

Spain contests the UK's claim to Gibraltar and draft EU Brexit negotiating guidelines have sparked a row over the British overseas territory.

The guidelines said: "After the United Kingdom leaves the Union, no agreement between the EU and the United Kingdom may apply to the territory of Gibraltar without the agreement between the Kingdom of Spain and the United Kingdom."