WARSAW (Reuters) - Poland's largest opposition party, tipped to win the country's Oct. 25 election, rallied behind its leader on Thursday after he warned that refugees from the Middle East could bring diseases and parasites to Poland.

Jaroslaw Kaczynski's comments have attracted wide criticism in the media and among the ruling centrists, with some saying he was using ultra-nationalist imagery to fan hatred and fear.

But the spokeswoman for Kaczynski's Law and Justice (PiS) party said there was nothing improper about his comments.

"(Jaroslaw Kaczynski) is talking about facts and asking whether there are real risks. This is what Poles are asking about. With millions of refugees (coming to Europe) such questions are completely justified," Elzbieta Witek told reporters.

Kaczynski's conservatives have used the refugee crisis in Europe to tap into deep-seated mistrust of foreigners in Poland in their bid to retake power after the election.

He took their rhetoric to a new level on Monday during a campaign stop in a small town 90 km (56 miles) north of Warsaw.

"There are already signs of emergence of diseases that are highly dangerous and have not been seen in Europe for a long time: cholera on the Greek islands, dysentery in Vienna. There is also talk about other, even more severe diseases," he said.

"Also there are some differences related to geography, various parasites, protozoa that are common and are not dangerous in the bodies of these people, (but) may be dangerous here. Which doesn't mean there is a need to discriminate anyone, but you need to check."

European health authorities have not reported any evidence of widespread outbreaks of infectious diseases in parts of Europe with high numbers of migrants.

Last month, Warsaw backed a European Union plan to share out 120,000 refugees across the 28-nation bloc. Under the plan Poland will take in 4,500 refugees, adding to some 2,000 it has already accepted.

But senior PiS officials have suggested they would oppose the relocation of migrants from war-torn Syria or Iraq to Poland if they win power, raising the prospect of further battles in Brussels on the politically toxic refugee issue.

(Reporting by Marcin Goclowski, Agnieszka Barteczko and Anna Koper; Editing by Tom Heneghan)