President Emmanuel Macron says France will not allow a new migrant camp to be set up in Calais, on a visit to the port where many gather, hoping to get to the UK.
Up to 700 migrants are congregating in the area, despite the camp known as the Jungle having been dismantled in 2016.
Mr Macron also vowed to punish officers involved in violence against migrants.
On Thursday, he will travel to Britain, where he is expected to demand the UK government does more to help.
In his first official visit to Calais, Mr Macron met migrants and groups working with them, as well as residents and local authorities who have called for more measures to prevent another large camp from emerging.
Two groups refused to meet the president in protest at strict measures used by the French police against migrants.
Mr Macron defended the security forces from accusations of brutality made by some activists, but vowed to take action against wrongdoings.
The Calais ‘Jungle’ became the French symbol of the European migrant crisis, and some 7,000 people – most from the Middle East and Africa – were living there before the area was cleared.
“In no case will we allow another Jungle here,” Mr Macron said on Tuesday.
France received a record 100,000 asylum claims in 2017, making it one of the main destinations in Europe.
The president is expected to unveil a new migrant policy next month, which will include speeding up the application process for asylum seekers and faster removal of those who fail to be accepted.
Macron to tell May: Do more
During last year’s French election campaign, Mr Macron said he wanted to renegotiate or scrap the 2003 Le Touquet agreement, which established French border controls in Britain and UK controls in Calais.
As a result, undocumented migrants barred from entering the UK stay in France –
Mr Macron will demand the UK do more to help ease the migrant burden when he meets British Prime Minister Theresa May on Thursday, French officials say.
He will ask the UK to allow in unaccompanied children and adults with family members already in the country and more money to help with border security.