CHISINAU (Reuters) - Leaders of a new pro-Russian electoral bloc opposed to Moldovan President Maia Sandu's plans to seek European Union membership said on Tuesday they were deliberately delayed and harassed at the airport on their return home.

Opposition parties, meeting at the weekend in Moscow, about 1,500 km (900 miles) from Chisinau, announced the formation of a bloc dubbed "Victory" to take part in a presidential election and a referendum on EU membership set for October.

The parties were grouped around fugitive pro-Russian business magnate Ilan Shor, sentenced in absentia last year to 15 years in prison for mass fraud.

"It's dreadful, coming back to your own country and not being able to head home," Irina Lozovan of the pro-Russian Renewal Party, linked to Shor, wrote on social media.

Moldovan media quoted eyewitnesses at Chisinau airport as saying that the party's chair, Natalia Parasca, was taken away for questioning by security service officers.

Lozovan later told Russian media that the returning politicians were eventually allowed to leave.

Officials said the delay was caused by "technical reasons", but passengers from other flights were seen leaving the airport without difficulty.

Sandu has denounced Moscow's invasion of Ukraine and declared Russia and corruption to be the two biggest threats to her country lying between Ukraine and EU member Romania.

She has made the campaign for EU membership for Moldova, one of Europe's poorest countries, the cornerstone of her policies.

Shor, who lives in exile in Israel was sentenced in connection with the disappearance of $1 billion from the Moldovan banking system in 2014, dubbed Moldova's theft of the century. Moldova has repeatedly sought his extradition.

Writing on Telegram, he said the returning politicians had been detained for several hours "without any grounds whatsoever" and accused he president of "abusing people".

Sandu's chief of staff, Adrian Balutal, writing on Facebook, said the pro-Russian politicians had shown themselves to be "servants of the Kremlin regime. But Moldovans are a wise people and will not allow bandits of any sort to take hold of our country and bring it to its knees."

(Reporting by Alexander Tanas; Editing by Ron Popeski and Jonathan Oatis)

By Alexander Tanas