Federica Mogherini, the European Union’s foreign-policy chief, must stay directly involved in talks between Kosovo and Serbia if the dialogue is to succeed, Hashim Thaci, the country’s foreign minister, said Thursday.

To lock in the reconciliation between the two former foes, Kosovo and Serbia should also start work on a second agreement in the new year, Mr. Thaci said in a sit-down with The Wall Street Journal in Brussels. Mr. Thaci, who was Kosovo’s prime minister for seven years until earlier this month, is still widely considered the country’s most powerful politician.

Ms. Mogherini, who took office on Nov. 1, has placed the Balkans at the top of her agenda in her first weeks in Brussels. On Monday, she confirmed she would convene a meeting of Kosovo and Serbian leaders in January, resuming reconciliation talks that have lapsed for much of 2014.

However Ms. Mogherini hasn’t said whether she will play the same role as her predecessor — Catherine Ashton — who personally led more than 20 meetings between Serbia and Kosovo leaders. Those talks helped pave the way for a landmark agreement between Pristina and Belgrade in April 2013, which sought to normalize the situation of the Serbian minority in Albanian-majority Kosovo.

“I understand Mogherini has a very wide agenda, but the EU’s backyard of Balkans has to be on the top of the priorities for the EU,” Mr. Thaci said soon after meeting the EU foreign-policy chief. “If we want success, Mogherini has to be in the room at the highest meetings. She has to lead the discussions.”

The Italian foreign-policy chief has her hands full as she looks to set a different imprimatur on the EU post than Ms. Ashton. While she has been on the road constantly, Ms, Mogherini has been far more involved in the work of the European Commission, the EU’s executive. She hopes thereby to combine the EU’s trade, aid and diplomatic leverage in its relations with non-EU partners.

Whereas Ms. Ashton spent huge amounts of personal time on a few files — including the Kosovo talks and negotiations on halting Iran’s nuclear program — Ms. Mogherini has indicated she wants to operate more broadly. In a statement after meeting Mr. Thaci on Thursday, Ms. Mogherini said that “for the EU and for me personally this remains a high prioritiy.”

Mr. Thaci said he expects the Serbia talks to resume in Brussels in the second half of January. It is possible that he and Serbian Foreign Minister Ivica Dacic will attend the meeting along as Serbian Prime Minister Aleksandar Vucic and Kosovo’s new premier, Isa Mustafa.

While the Kosovo-Serbia dialogue made big progress in 2013 — paving the way for the EU to start membership talks in January this year and for Kosovo to close in on a a pre-accession accord with Brussels — progress has slowed this year. Elections first in Serbia and then in Kosovo in June put the dialogue on hold. Kosovo’s six-month political crisis as politicians failed to approve a new government further delayed serious work.

Mr. Thaci, who met with the Serbian prime minister in New York for a long one-on-one meeting two weeks ago, said he sees work continuing in parallel on implementing the remaining gaps in the April 2013 accord and on a new agreement.

Serbia has vowed never to recognize the 2008 independence of its former province. However the EU has set a normalization of ties as a precondition for the country’s entry into the EU. The EU has also said neither government should block the other on its EU path.

Mr. Thaci said it will be for Ms. Mogherini to set out the reference terms for a second agreement. But he said it must include a commitment from Serbia not to block Kosovo’s membership in regional, European and global organizations.

“I believe that this will be reached in the new agreement because I think it has become part of conditionality also to the Serbian path to EU integration,” he said.

Kosovo is recognized by more than 100 countries, but not by Serbia, Russia and China as well as five EU member states, including Spain and Romania. Serbia insisted the 2013 agreement with Kosovo was stripped of a provision committing Belgrade not to lobby against Kosovo’s admission to global bodies such as the United Nations.

Kosovo recently won membership in the Olympics, as it pushes recognition in a range of political, cultural and sporting clubs. Mr. Thaci said he hopes to attend the 2016 games in Rio de Janeiro, where Kosovo’s flag will fly for the first time.

“I was in London, but we had no participants. In Rio, we shall cheer for our team,” Mr. Thaci said.

Mr. Thaci said he hopes Kosovo will sign its pre-accession Stabilization and Association Agreement with EU in the “next months.” Brussels has said the country must make progress on rooting out widespread corruption and strengthen the rule of law.

He also expressed frustration over the slow pace of talks aimed to make it easier for Kosovo citizens to travel to the EU. “I have no nostalgia for Tito,” he said, referring to the former Yugoslav strongman who died in 1980. “But it’s ironic that Kosovars were able to move more freely more than 30 years ago than today in Europe.”