Trump's tweet, issued shortly after he arrived in the French capital Paris, comes days after French President Emmanuel Macron suggested that Europe should create its own army to protect itself from potential enemies including Russia, China - and the United States.
Nevertheless, a senior French source said: "It's really important to have the British on board, not just because they have the most capable, rapidly deployable armed forces along with our own, but also because we share the same strategic culture and history of projecting force outside Europe".
"I don't think that this defense identity will start with an European Union army", Schinas said on Tuesday. "I've seen what they have planned, and I think it's going to be something very, very special".
Mr Trump ordered the Pentagon to come up with plans for his own version, but they were eventually scrapped over concerns about costs and the damage tanks weighing many tons would do to the streets in Washington.
In addition to his meetings with Macron, Trump is expected to visit the Belleau Wood battlefield and American cemetery on Saturday, and speak at a Veterans Day ceremony Sunday at the Suresnes American Cemetery.
"Faced with Russian Federation, which is near our borders and has shown it could be threatening - I want to build a real security dialog with Russian Federation, which is a country I respect, a European country - but we must have a Europe that can defend itself on its own without relying only on the United States".More news: The Florida Governor’s Race Is Probably Headed for a Recount
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Macron's office declined to comment on Trump's tweet.
"I don't know that we're seeing each other in Paris, but we may", Trump said. European leaders say maintaining trade ties is essential to keep Iran from exiting the deal and restarting development of nuclear weapons. That now seems more likely for later this month, when they attend the Group of 20 summit of global leaders in Argentina. "There may be a lunch for the leaders".
At the same time, Macron has increasingly been positioning himself as a bulwark against the rising tide of Trump-style populism across Europe, speaking out loudly against the dangers of nationalism and isolationist retreat.
Macron had made the remark Tuesday but Trump waited until he was in town to trash talk the French president.
Macron and other European leaders have repeatedly criticized Trump's efforts to undermine the deal, and have sought to create a special mechanism that would allow the bloc to avert USA sanctions and continue trading with Iran. The pair are expected to meet during the G-20 meeting later this month in Argentina, and the White House has invited Putin to visit Washington.
The dividends of Macron's cultivation of Trump are "modest at best", said Stewart M. Patrick, a fellow at the Council on Foreign Relations.