Prominent Kremlin critic and former opposition lawmaker Dmitry Gudkov said on Sunday he had left Russia for Ukraine due to pressure from authorities ahead of the September parliamentary elections.
Gudkov's departure comes as the Russian opposition says the authorities are stepping up a campaign of intimidation against dissenters and potential challengers, claims the Kremlin has rejected.
"I am approaching Kiev," Gudkov, 41, said on Facebook in a post he confirmed to AFP as genuine.
He said sources close to the Kremlin told him that if he did not leave he would be arrested over a "fake" criminal case against him.
"My decision has been supported by my relatives and loved ones who have also received serious information about threats and risks," wrote Gudkov.
The Kremlin critic's father, Gennady Gudkov, who is also a former opposition lawmaker, said that he backed his son's decision to "temporarily leave the country."
Gudkov had announced earlier this year he planned to run for parliament.
He had been detained earlier this week, a day after another well-known anti-Kremlin campaigner, Andrei Pivovarov, 39, was yanked off a Warsaw-bound plane in Saint Petersburg minutes before takeoff.
Gudkov was detained over unpaid rent from 2015 and faced up to five years in prison. He and his supporters have called the criminal case a form of punishment for his plans to take part in elections.
But he was suddenly released without charges on Thursday evening in a rare about-face by Russian authorities.
His lawyer Mikhail Biryukov has told AFP that the opposition politician had been set free without being formally charged.
Gudkov, a former member of the A Just Russia party, however, remains a suspect.
- Pressure grows -
Kremlin critic Pivovarov remains in jail, after a court this week ordered that he be held in pre-trial detention for two months.
Pivovarov, the former executive director of recently disbanded pro-democracy group Open Russia, was pulled off a Warsaw-bound flight on Monday as his plane was taxiing toward take-off.
A criminal probe was launched against the activist for cooperating with an "undesirable organization", and he faces up to six years in prison if convicted.
Open Russia, founded by self-exiled Putin critic Mikhail Khodorkovsky, announced last week it was shutting down to shield its members from prosecution.
The group was designated an "undesirable" organization in Russia in 2017 in line with a law targeting foreign-funded groups accused of political meddling.
A court in Moscow is considering whether to designate jailed Kremlin critic Alexei Navalny's political network as an "extremist" organization, which would remove a key challenger to the ruling United Russia party. A decision is expected as early as next week.
Navalny, the most prominent Putin opponent to emerge in recent years, was himself imprisoned in February on old fraud charges.
On Friday, Putin approved an anti-extremism law expected to be used to ban his allies from running in elections. The Kremlin chief signed off on the legislation the day Navalny marked his 45th birthday behind bars.
Many of his close allies are either outside Russia or under arrest.