After a White House meeting with German Chancellor Angela Merkel, U.S. President Donald Trump said he supported NATO but renewed a call for member nations to increase their financial contributions to support the military alliance.
Trump expressed his "strong support for NATO" but called on fellow members who "owe vast sums money" to "pay their fair share."
WATCH: Trump: NATO Members 'Must Pay Fair Share'
His remarks came at a news conference after an Oval Office meeting with Merkel, a key ally he accused of "ruining" Germany by admitting thousands of Syrian refugees.
It was the first in-person meeting between the leaders of the Western world's most influential countries since Trump's election, and one that could help shape the future of the transatlantic alliance.
They were seemingly on a collision course since candidate Trump accused Merkel of "ruining" Germany and other European countries with liberal immigration policies, spoke ill of NATO and hinted at a trade war.
Merkel, for her part, scolded Trump for imposing a travel ban on immigrants from six Muslim-majority countries, and she reminded him that any close U.S.-Germany cooperation must be based on "values of democracy, freedom, respect for the rule of law and human dignity, regardless of origin, skin color, religion, gender, sexual orientation or political belief."
Trump said the relationship between the U.S. and Germany was built on "shared values" and the alliance was a "symbol of strength" to the world.
In addition to NATO, several other contentious issues awaited the two leaders. Trump said he appreciated Germany's support in addressing the conflict in Ukraine, where "we seek a peaceful solution."
Trump said the two countries would continue the fight against "radical Islamic terrorism," saying "immigration security is national security."
The two leaders were to have a working lunch at the White House, where the president said "fair and reciprocal" trade policies would be discussed.
WATCH: Merkel: 'Hope We Can Resume' US-EU Trade Agreement Talks
As a candidate, Trump suggested he would renounce multilateral deals, such as the Transatlantic Trade and Investment Partnership (T-TIP) with Europe, which had been championed by Merkel and former U.S. President Barack Obama.
In a hint at a possible compromise, a senior administration official told reporters last week that T-TIP could be considered a one-on-one trade deal, given how the EU structure interconnects European economies.
The leaders were also expected to discuss another controversial issue, Trump's proposed border tax, which is meant to encourage companies to make goods in the United States. Just hours before the Oval Office meeting, Germany's economy minister threatened to sue the U.S. at the World Trade Organization in an attempt to block the tax.
Trump sees the tax as boosting his job-creation agenda. Europeans see it as a challenge to the global trading system at a time when Trump's policies are pushing the United States toward protectionism.
Daniel Hamilton, director of the Center for Transatlantic Relations at the Johns Hopkins University School of Advanced International Studies, sees the White House meeting as a prelude to future negotiations.
Trump makes his first presidential visit to Europe in May to attend both a NATO summit in Brussels and a Group of Seven summit in Sicily. "That will be the next big step," Hamilton said.
Merkel and Trump were originally scheduled to meet earlier this week, but a snowstorm on the U.S. East Coast prompted the two world leaders to delay the session.