French President Emmanuel Macron said it is "obvious and indispensable" to have exchanges with US President Donald Trump as the two leaders were set to try to find common ground on security, defence and other issues.
Mr Macron spoke at a news conference following a meeting in Paris with German Chancellor Angela Merkel who, like Mr Macron, was deeply disappointed in Mr Trump's recent decision to withdraw the US from a global agreement to combat climate change.
Ms Merkel said differences with the US are "regrettable" but that communication continues.
Mr Trump arrived in the French capital on Thursday after an overnight flight from Washington for a whirlwind 36-hour visit to meet with Mr Macron and tackle potential solutions to the crisis in Syria and discuss broader counter-terrorism strategies.
Mr Macron and his wife Brigitte greeted Mr Trump and first lady Melania Trump at Les Invalides, site of Napoleon's tomb.
Mr Trump planned to participate in Bastille Day celebrations on Friday and commemorate the 100th anniversary of the US entry into the First World War before returning to Washington.
The president's decision last month to withdraw the US from the Paris climate accord sparked outrage across Europe, and anti-Trump protests are planned while he is in Paris.
Mr Macron, a staunch advocate of research to combat global warming, has beckoned "all responsible citizens", including American scientists and researchers, to bring their fight against climate change to France.
Mr Trump said the climate deal was unfair to the US.
Mr Trump, Ms Merkel, Mr Macron and other leaders met in Hamburg, Germany, last week during a summit of the world's leading rich and developing nations.
Ms Merkel and Mr Macron met again in Paris on Thursday before Mr Macron's meeting with Mr Trump.
Mr Trump and Ms Merkel were not expected to meet.
Ms Merkel said during a joint appearance with Mr Macron that it is important to keep talking with Mr Trump even where the differences are clear.
She said last week's summit showed that common ground exists, for example, on fighting terrorism, but that "we also had to name clear differences, for instance regrettably the difference on whether we need the Paris climate accord or not".
She added: "We did not paper over these differences, but nevertheless contact, the ability to speak is of course important."
Mr Macron said Germany and France agree on the importance of close ties with the United States, despite the differences.
Mr Trump and Mr Macron also planned a joint news conference on Thursday after their talks, where Mr Trump may be asked to respond to Ms Merkel and to questions about emails showing that his eldest son Donald Trump Jr welcomed the prospect of receiving Russian government support in last year's presidential campaign between his father and Hillary Clinton.
The visit to Paris could offer Mr Trump a brief distraction from the controversy.
However, he is visiting a city he has repeatedly disparaged.
When he announced his decision on the climate agreement, Mr Trump said he was "elected to represent the citizens of Pittsburgh, not Paris".
He has also repeatedly said the city has been ruined by the threat of terrorism, which he ties to immigrants.
"Paris isn't Paris any longer," he said in February.
But counter-terrorism issues give Mr Macron and Mr Trump the potential for a strong working relationship.
Mr Macron's national security pitch has not differed drastically from Mr Trump's.
On Syria, he argues for intervention, saying that President Bashar Assad is a threat to Syria and the Islamic State group is a threat to France.
France has been plagued in recent years by extremist attacks.
During last year's Bastille Day celebrations, a 19-ton cargo truck deliberately ploughed into crowds in Nice, killing more than 80 people.
Mr Macron supports intervention against Syria's government in response to its use of chemical weapons and could prove an important ally as the Trump administration seeks to increase pressure against Mr Assad.
However, in doing so, they will need to tackle the issue of Russia's support for Mr Assad, something Mr Trump has only passively acknowledged.