Ukrainian border guards and police turned up at a hotel in the city of Lviv where Mr Saakashvili was staying and presented him with an official document detailing his alleged violation of crossing the border illegally.
"They did it against all the rules, what's happening here?" Surrounded by supporters, he broke through a cordon of Ukrainian border guards in chaotic scenes at the Ukraine-Poland border Sunday.
Earlier, Georgia sent the Ukrainian Prosecutor General two requests for the arrest and extradition of Saakashvili.
Saakashvili denies the accusations branding them a political witch hunt. Ukraine refused to extradite former President of Georgia because charges against him are politically motivated, the Ukrainian Prosecutor-General's office said.
The narrative Saakashvili is putting out is that Poroshenko and his government is corrupt, oligarchs are shooting for just an image of Reform, and his new party is the vehicle to bring real change to Ukraine.
Ukraine's outspoken ex-prime minister Yulia Tymoshenko threw her support behind the 49-year-old, accompanying him as he attempted to cross into Ukraine the first time. Ukrainian authorities had previously stopped him from entering the country by train earlier that day.
Romania, meanwhile, said "the need to conform with global norms on promoting and protecting the rights of people who belong to the Romanian national minority in Ukraine has been continually pointed out" in talks with Kiev.
Ukrainian Minister for Foreign Affairs Pavlo Klimkin poses during an interview in Paris
"We continue to regard as shameful and outrageous the new education Act, which drastically restricts the access of minorities.to native language teaching in a manner that makes that practically impossible from the age of 10 and is incompatible with European values and regulations", Mr Szijjarto said.
The charismatic Saakashvili is credited with pushing through pro-Western and anti-graft reforms in Georgia which he led from 2004 to 2013.
Saakashvili divides opinion in Ukraine, which is at war with Russia-backed rebels in its east.
He was president at the time of a five-day war with Russian Federation in 2008, a conflict his critics argued was the result of his own miscalculations.
"Mikheil Saakashvili is the political past of our country, a very sad past, and it is very unfortunate, what we see now [in Ukraine]".
Poroshenko stripped Saakashvili of his citizenship in July, making him stateless.
Saakashvili says he does not covet the presidency himself and wants to promote a new, younger politician to the post.