The United Nations on Monday urged Lebanon's politicians to act responsibly to protect Lebanon's stability following elections that saw allies of the Iran-backed Hezbollah group make gains.

"We hope that all Lebanese political stakeholders will continue to act responsibly in the days following polling to protect Lebanon's stability, which should include the swift formation of a government," said UN spokesman Stephane Dujarric.

The Shia Hezbollah was set to cement its dominance in Lebanon after the party of its main rival, Prime Minister Saad Hariri, suffered heavy losses.

Formed in the 1980s to fight against Israel, Hezbollah currently battles in Syria alongside President Bashar al-Assad's forces. It is listed as a terror organisation by the United States.

Hezbollah members were accused over the 2005 assassination of Hariri's father Rafiq, a charismatic former prime minister.