German Chancellor Angela Merkel, second from right, and French President Emmanuel Macron, right, greet Serbian President Aleksandar Vucic and Serbian Prime Minister Ana Brnabic upon their arrival Monday in Berlin for a conference on western Balkan nations. (Carsten Koall/Getty Images)

European leaders pushed Serbia and Kosovo on Monday to step back from a potential new conflict and return to peace talks, while Kosovo’s divided political leadership came together briefly to seek help from the United States.

German Chancellor Angela Merkel and French President Emmanuel Macron held lengthy but inconclusive talks in Berlin with leaders of Serbia and Kosovo, seeking to reduce nationalist tensions on both sides that derailed peace talks led by the European Union. All sides plan to meet again July 1 in Paris, Kosovo President Hashim Thaci said in an interview.

Both European leaders tamped down expectations for quick progress, and Thaci said European Union members cannot agree among themselves about how to deal with the Balkan tensions.

“Without the United States we can do no final agreement, because the E.U. is divided, it’s true,” Thaci said by phone from Berlin, after meetings and a dinner among the European and Balkan leaders that he called “difficult” but cordial.

Kosovo broke away from Serbia and declared independence in 2008 with backing from the United States. The Trump administration supports the E.U. reconciliation process but has also broken with Merkel to say that adjustments to the Serbia-Kosovo border could be considered if both countries agree.

Before attending the European talks, Kosovo’s sometimes-feuding leaders united for an unprecedented joint meeting with the U.S. ambassador to Germany, Richard Grenell, whom Thaci has sought out as a go-between with close ties to President Trump.

“The President, Prime Minister, and Foreign Minister of Kosovo requested a meeting with us,” a statement from the U.S. Embassy said. “This was a follow up to an earlier visit by President Thaci. The United States continues to strongly support the EU-facilitated dialogue between Kosovo and Serbia.”

A U.S. official said Grenell reiterated that Kosovo should suspend punitive tariffs on Serb goods, the same message Kosovo leaders also heard from a top State Department official who visited the country last month.

Thaci had pledged to Grenell this year that he would work to dismiss the tariffs imposed in November, but Thaci’s internal political rival, Kosovo Prime Minister Ramush Haradinaj, the former leader of the Kosovo Liberation Army, has not publicly agreed.

The two politicians, who are from different political parties, have separately appealed to Washington to take a more central role.

Washington wants the two to act in concert to rescind the 100 percent import tax on Serb goods. The tariff was imposed in retaliation for what Kosovo said was Serbia’s efforts to sabotage marks of international recognition, including membership in Interpol.

“Ambassador Grenell was forceful on suspending tariffs and reiterated that the United States is a close friend of Kosovo and wants to help where possible, but that the two parties themselves had to come up with the details, not the United States,” said the U.S. official, who spoke on the condition of anonymity to discuss the closed diplomatic meeting.

Trump had dangled the possibility of a White House peace signing if the two countries could come together, writing to the Serb and Kosovo leaders separately in December to encourage them to talk.

The E.U. has told Serbia and Kosovo that they must improve relations before they can join the bloc, but the E.U.-led negotiations have meandered for more than seven years.

Serbia has refused to return to the table until the tariffs are lifted.

Ahead of the Berlin meeting, Serb officials also downplayed chances that the European leaders could produce much progress. Merkel is “playing for time” because she remains opposed to even slight adjustments to the land border between Serbia and Kosovo, seeing it as a bad precedent that undermines European unity, one Serb official said.

Serbian President Aleksandar Vucic is thought to quietly support land swaps to adjust the border along mostly ethnic lines, although he told reporters Monday that “we are against border changes but are ready to talk about all possible solutions.”

Thaci said the Berlin talks did not include “any substantial discussion” of borders.

More than 10,000 were killed in a war between Serbia and breakaway Kosovo in 1998 and 1999. NATO launched an air campaign in 1999 to end the conflict.

Kosovo’s subsequent declaration of independence won support from the United States and most European Union nations. Russia, a patron of Serbia, does not recognize Kosovo.