By Anita Komuves

BUDAPEST (Reuters) - Central European nations should unite to preserve their Christian roots as western Europe experiments with same-sex families, immigration and atheism, Hungarian Prime Minister Viktor Orban said on Thursday. Orban, a nationalist who has been in power for more than a decade, was speaking at an event to inaugurate a monument commemorating the Treaty of Trianon, which was signed after World War One and led to Europe's maps being re-drawn.

"Western Europe had given up on ... a Christian Europe, and instead experiments with a godless cosmos, rainbow families, migration and open societies," Orban said in a speech.

He said the monument, a 100-metre long and 4-metre wide ramp carved into a street near Budapest's parliament building, was a call to central European nations to strengthen their alliance and rally around what he called the "Polish flagship".

In Poland, Hungary's main ally in central Europe, the ruling Law and Justice party (PiS) has pursued a socially conservative platform since coming to power in 2015 and made opposing "LGBT ideology" a key plank of its electoral strategy.

In Hungary, rights groups say hostility to LGBT+ people has increased since Orban won a third term in 2018. Orban himself had rarely criticised rainbow, or same-sex families, but Parliament's speaker - a long-time ally of Orban - had equated gay adoption with paedophilia.