WARSAW - Nationalist opposition party Law and Justice (PiS) came first in Poland's local elections, an exit poll showed on Sunday, in a setback for Prime Minister Donald Tusk's ambitions to cement his grip on power.

If confirmed, the results would dash Tusk's hopes of leading his Civic Coalition (KO) grouping to first place in the election independently of its partners in the ruling coalition.

While PiS came in ahead of KO, it was still well behind the combined score of the three groupings that make up the coalition government.

PiS scored 33.7%, according to the Ipsos exit poll, ahead of KO, which had 31.9%.

The other groupings in government, the centre-right Third Way and the Left scored 13.5% and 6.8% respectively.

Poles were voting to choose the members of 16 regional assemblies - whose composition roughly reflects support for the main parties - as well as thousands of local councillors and mayors.

Tusk swept to power following a national election in October on promises to reverse democratic backsliding, boost the rights of women and minorities and repair ties with Poland's Western allies that had become strained under the previous government.

PiS came first in October's election but lost its majority, and of late the party and its allies have been plagued by infighting.

Brussels is closely watching how Tusk's coalition fares as it faces European Parliament elections in June. Europe-wide opinion polls suggest the populist right will perform well. REUTERS