MOSCOW (AP) — Ukraine's president on Monday criticized former governor Mikhail Saakashvili for illegally crossing into Ukraine from Poland.

Saakashvili and a small crowd of supporters on Sunday shoved their way through a line of guards at the Ukrainian border, making good on the politician's vow to return to the country that had stripped him of his Ukrainian citizenship.

Saakashvili, who became governor of Ukraine's Odessa region after being Georgia's president from 2004 to 2013, poses a strong challenge to Ukrainian President Petro Poroshenko, who once was Saakashvili's patron but then revoked his citizenship in July.

Poroshenko condemned Saakashvili on Monday for crossing the border without proper documents and said law enforcement agencies should look into the incident.

He said Saakashvili should have contested the decree stripping him of citizenship in court if he disagreed with it.

"But instead, he committed a crime — because the state border must not be violated," Poroshenko said.

Speaking to reporters in the western city of Lviv later Monday, Saakashvili rejected the accusations, saying that stripping him of Ukrainian citizenship "was the crime."

Saakashvili was appointed to the Odessa post in 2015 on the strength of his record of fighting corruption in Georgia. But he resigned after only 18 months, complaining that official corruption in Ukraine was so entrenched he couldn't work effectively.

The return carries risks for Saakashvili, who is stateless. He gave up his Georgian citizenship when he got the job in Ukraine. Georgia, where he faces accusations of abuse of power and misappropriation of property, has sent an extradition request to Ukraine. It's not clear if Ukraine intends to honor it.