Brexit and the security situation in the wake of the Westminster terror attack are set to dominate London Mayor Sadiq Khan's three-day visit to Brussels and Paris.
Mr Khan will hold talks with European Council president Donald Tusk when he arrives in the Belgian capital on Monday before delivering a keynote address in the city on Tuesday, ahead of travelling to Paris.
With Prime Minister Theresa May set to formally trigger Brexit negotiations on Wednesday, Mr Khan said he wants to use the trip to drive home the message that London will remain open for European business and investment after the UK's withdrawal from the EU.
Mr Khan is also seeking to learn security lessons from Brussels and Paris in the aftermath of the Westminster attack as both cities have suffered major terrorist atrocities in the past two years.
The mayor will meet Britain's EU commissioner, Sir Julian King, who holds the security portfolio, in Brussels, and then the French interior minister, Matthias Fekl, in Paris.
Mr Khan said: "This will be a vital chance to strengthen London's ties still further with Paris and Brussels.
"I will be meeting politicians, officials and business leaders, and I look forward to discussing a variety of key issues with them, ranging from Brexit and expanding London's economy, to air quality, social integration, and security.
"Both Brussels and Paris have, of course, been the victim of recent terror atrocities.
"In the wake of the horrific attack in Westminster last week, it will be an opportunity to learn from each other and to show solidarity in the face of this evil assault on our shared values and way of life.
"Like the people of Brussels, and Parisians, Londoners will never be cowed by terrorism."
While in Brussels, Mr Khan will also meet Jean-Claude Juncker, president of the European Commission, European Parliament president Antonio Tajani, and the European Parliament's Brexit negotiator, Guy Verhofstadt.