* Minister says case against him is politically motivated
* Minister Omelyan helped bring Ryanair to Ukraine this year
* Ukraine holds elections next year (Adds minister's comments, prosecutor interview)
By Olena Vasina and Natalia Zinets
KIEV, Sept 13 (Reuters) - Ukraine's infrastructure minister, who oversaw the entry of Ryanair into the country this year, is under investigation on suspicion of illegal enrichment, anti-graft officials said on Thursday, but he denied any wrongdoing.
The probe into Infrastructure Minister Volodymyr Omelyan is the highest-profile case since the creation of a national anti-corruption bureau (NABU) after protests in 2014 brought a pro-Western government to power promising sweeping reforms.
Omelyan strongly defended his record and refused to resign, adding that the investigation was politically motivated and intended to discredit the government ahead of elections in 2019.
"I categorically reject all accusations brought against me," Omelyan told a news conference. "I want to say that I am being pressured by the leadership of the NABU.
"I know the facts of political cooperation between the leadership of NABU and Ukrainian politicians," he added.
Nazar Kholodnytskyi, the top prosecutor in charge of corruption cases, denied the case was politically motivated and said it was for the court to judge whether Omelyan was guilty.
In the run-up to next year's presidential and parliamentary elections, he told Reuters, "any of our investigations... will be seen as political reprisals or orders, or something else".
"If the investigation does not prove any crime in the actions of Minister Omelyan within two months, the investigation will be closed," Kholodnytskyi added.
NABU detectives notified Omelyan of the investigation on Thursday morning, saying that his assets, which include $90,000 in cash and a BMW car, exceeded what he would have earned as a civil servant since the year 2000.
They also allege that he did not declare assets worth hundreds of thousands of dollars across 2015 and 2016, including a BMW, the cost of renting the home that he lived in, and the cost of a country residence and land that he also used.
Omelyan helped bring Ryanair to Ukraine in March, something the government hailed as a showcase example of Kiev making life easier for foreign investors despite problems of corruption and the influence of oligarchs over the economy.
Prosecutors and NABU, whose investigators were trained by the U.S. FBI, have called on Omelyan to pay a 5 million hryvnia ($177,872) bond pending the outcome of the case, and a court will decide whether to approve the request.
Omelyan told Reuters in an interview in March that he expected legal cases to be opened against him because he is helping to drive reforms that aim to liberalise the ex-Soviet republic's economy, purge corruption and improve governance.
"But it's normal. It's Ukraine. It's my headache," he said at the time.
Omelyan's party, the People's Front, said the case against him had been launched because "elections have started in Ukraine". It urged anti-graft agencies to stay out of politics. ($1 = 28.1100 hryvnias) (Writing and additional reporting by Matthias Williams Editing by Gareth Jones)