BERLIN (AP) - The leaders of Germany and France called for vigilance Friday to prevent the spread of a coronavirus variant that this week prompted Britain to delay the planned relaxation of pandemic restrictions in England.

Chancellor Angela Merkel said that while Germany has very low numbers of new COVID-19 infections at present, the “aggressive” delta variant could lead to a rise in new cases.

“We can't pretend that corona is over,” Merkel told reporters in Berlin.

“Even though there's a feeling on such a warm summer's evening that it's all over, one can see from the example of Lisbon that things can quickly change,” she said. “That's why I think it's necessary to be careful, so that we have a summer with many freedoms but not yet all freedoms.”

Portuguese authorities on Thursday banned travel in or out of the capital region over coming weekends in response to a spike in delta variant cases. Earlier this week, British Prime Minister Boris Johnson pushed back the date for lifting restrictions on social contacts by four weeks as the government reported thousands of newly confirmed cases, mostly with the delta variant.

Asked about travel related to the Euro2020 soccer tournament, Merkel said it was good to see thousands of fans at the recent Germany-France match in Munich again.

“But when I see completely full stadiums in other European countries, then I'm a bit skeptical whether that's the right answer to the current situation,” she said - a reference to Hungary, where authorities have allowed games without limiting spectator numbers.

Merkel spoke ahead of a working dinner with French President Emmanuel Macron, the first time she has hosted a foreign leader in Germany since last year.

Macron said it was important to be vigilant about the new variant and the European Union would discuss at an upcoming summit how to better harmonize travel restrictions during the pandemic - something the bloc has struggled to do more than a year after the start of the outbreak.

EU countries have administered at least one dose of vaccine to roughly half of their populations, while more than a third have received both shots. Britain, which left the bloc last year, has a higher vaccination rate.

Aside from the pandemic, next week's EU summit will also address foreign policy issues such as the bloc's relationships with Russia and Turkey, and the future of its common defense and security policy.

Macron welcomed U.S. President Joe Biden's commitment to NATO.

“I think we succeeded in establishing the idea that European defense and EU strategic autonomy is not an alternative to the trans-Atlantic organization, but a solid component of it,” Macron said of the recent meetings with Biden at the Group of Seven and NATO.

Merkel concurred. “We can all be glad that (Biden) has created a climate of cooperation again, in which everyone of course has their role to play,” she said.

“But I see an absolute necessity - and this is something I believe the United States expects - that we act coherently, that we say which areas of work we can take on and which contribution we can make.”

Angela Charlton in Paris contributed to this report.