President Borut Pahor during a televised debate at Slovenia's public TV, in Ljubljana, Slovenia, October 19, 2017.  Photo: AP

The challenger in Slovenia's presidential election runoff has conceded defeat after ballot returns showed President Borut Pahor with an insurmountable lead.

Marjan Sarec, the mayor of the northern Slovenian town of Kamnik, said Sunday that he wished to congratulate Pahor on winning a second term in office.

Sarec is an ex-comedian and a relative newcomer to Slovenia's state politics, but he managed to put up a strong challenge to political veteran Pahor.

He said the support he received indicates that "it's time for change" and he was "proud to have had a possibility to run against the premiere league."