ABC News' Alexander Marquardt and Dragana Jovanovic report:

SIMFEROPOL, Crimea, Ukraine - Hundreds gathered here outside the central parliament building Thursday afternoon, kept at a distance by police because of the armed gunmen roaming the halls inside.

But the crowd was in little danger. They were there to express their support of the unidentified dozens who stormed the building in the early hours of Thursday and raised the Russian flag.

The ease with which they took the building and raised the Russian flag highlighted the deep divisions in Ukraine following the ousting of pro-Russia President Viktor Yanukovich and his government last week. It also fueled speculation of a possible attempt by the Crimean peninsula - about 500 miles from the Ukrainian capital of Kiev - to secede from Ukraine, or of Russian troops deploying in the region.

"We have chosen to side with Russia and we want [our leaders] to make a decision so we become part of Russia," said Anatoly Paramonov, standing outside the parliament building amid a crowd that chanted "Russia," "Putin," and sang Russian World War II victory songs.

Russia "is very close to us and we are in favor of a referendum" to determine Crimea's future, added Galina Kormanova, nearby. "I am a citizen of Ukraine, but I am Russian."

Russia's Black Sea Fleet is based on the peninsula with around 25,000 troops. Ukraine's acting president warned on Thursday that if the forces left the base it would be seen as an act of military aggression.

Credit: Viktor Drachev/AFP/Getty Images

Today's rally in Simferopol was defiant but also celebratory, at times. It transformed from mostly middle-aged people to a sea of youth in the afternoon.

Several hours after masked, armed men seized the government building in Simferopol, Crimea's parliament announced plans to hold an independence referendum on May 25, the same day as Ukraine's presidential election, on the autonomous peninsula's future.

The armed takeover followed a day of scuffles between rival factions of Crimean ethnic Tatars, who support the Kiev government, and members of the Russian-speaking population who reject Ukraine's caretaker government as an illegitimate coup. The clashes left two people dead.

More: Tension Rising in Pro-Russia Enclave Amid Ukrainian Unrest

Russia announced on Wednesday that it was launching a massive military exercise to test the combat readiness of some 150,000 troops. Fighter jets along Ukraine's border have been put on combat ready status.

"I expect Russia to be transparent about these activities and I urge them not to take any steps that could be misinterpreted or lead to miscalculation during a very delicate time, a time of great tension," said U.S. Secretary of Defense Chuck Hagel on Thursday at a NATO meeting in Brussels.

Russia denied the exercises are related to the turmoil in Ukraine and reportedly gave NATO and the U.S. advance warning before they began.

Secretary of State John Kerry downplayed the tensions following a conversation with his Russian counterpart, saying, "I don't think [the exercise] is something so prolonged that there is going to be an impact" in Ukraine.

As Ukraine announced the formation of a new interim government on Thursday, its former president re-surfaced after fleeing Kiev on Friday. In a statement, he rejected his impeachment while asking for protection from Russia.

"Unfortunately, what is happening in the Ukrainian Verkhovna Rada [parliament] is not legitimate," Yanukovich said. "I have been forced to ask the leadership of the Russian Federation to provide me with personal security from the actions of extremists."

Moscow agreed to protect Yanukovich, Russian news agencies reported, and Yanukovich also announced a press conference on Friday afternoon in the southern Russian city of Rostov-on-Don.