ROME (Reuters) - Italy’s far-right League made strong gains in a first round of mayoral elections on Sunday, while its coalition partner the 5-Star Movement struggled and the center-left lost further ground.

FILE PHOTO: League leader Matteo Salvini, now Italy's deputy prime minister, smiles as he arrives to attend a news conference, the day after Italy's parliamentary elections, in Milan, Italy March 5, 2018. REUTERS/Stefano Rellandini/File Photo

Some seven million Italians were eligible to elect mayors in 760 towns and cities, including 20 provincial capitals. Run-offs will be held on June 24 where no candidate reached 50 percent.

Candidates backed by the League won outright victories in Treviso and Vicenza in the north-east and were leading in numerous other cities where the incumbent mayor was from the center-left.

“I’m very happy, for the mayors ... and because we have reached the run-off in cities that have always been hard for us,” said League leader Matteo Salvini, who is deputy prime minister in Italy’s new coalition government.

The ballot was the first test of voter sentiment since the radical 5-Star/League coalition took power this month following an inconclusive March 4 election, promising to slash taxes, hike welfare spending and challenge European Union budget rules.

5-Star, which is by far the largest group in parliament and is Italy’s most popular party, according to opinion polls, fared poorly in the local elections. It reached the run-off in just three of the provincial capitals and leads only in the Sicilian city of Ragusa where it already had the incumbent mayor.

Despite breakthrough victories in the cities of Rome and Turin in 2016, 5-Star traditionally underperforms in mayoral votes. With its loose, internet-based format it lacks power bases and organization that bolster support at the local level.

The center-left Democratic Party, the big loser in the March 4 national vote, continued to shed support in the mayoral election.

The center-left, which held control of 15 of the 20 provincial capitals at stake and more than half of the 109 cities with more than 15,000 inhabitants, looks set to lose many of these at the June 24 run-off.

Despite a first-round victory in the northern city of Brescia, the center-left risks losing traditional Tuscan strongholds such as Pisa and Siena, and is excluded from the run-off in the Umbrian city of Terni.

It also lost badly to the center-right in the Sicilian city of Catania, where its incumbent mayor had held four terms of office.