Ukraine's government launched airstrikes Monday against pro-Russia separatists who seized the Donetsk airport following Sunday's presidential election. 

The rebels seized the airport in retaliation after Ukraine elected Petro Poroshenko, a pro-Europe billionaire who made his fortune in the candy industry, as the country's new president. 

On Monday, there there were explosions and gunfire at the airport while paratroopers landed in attempts to stop the violence. A security official said that it is one of the most violent clashes since fighting began in March between pro-Russia rebels and pro-Ukraine nationalists, according to The Telegraph. 

A spokesman for the Ukrainian joint forces said that a deadline passed at 1 p.m. for the rebels to stop the fighting, which is why jets were deployed. He said that two Sukhoi Su-25 jets fired warning shots around the Sergei Prokofiev International Airport in Donetsk. 

"In reply, the guerrillas opened fire at random from all types of weapon," he said. 

"Right now at the airport, paratroops have landed and are cleaning up the area," he added. 

A local news site published a photo of men in camouflage with a grenade launcher on top of the roof of the terminal who are reportedly separatist rebels. 

Three trucks were seen carrying rebels to the airport in the morning, and at least four men could be seen on the roof. Spokespeople of the Donetsk People's Republic, a pro-Russia militant group, said they have seized the airport and aim to wrest it from the government's military forces. 

Poroshenko said he would not negotiate with "terrorists," despite urging from Russia to stop its military operations in east Ukraine. However, he did say that he wants to broker peace with the insurgents and is willing to have talks with Moscow.  

Donetsk, a city of 1 million, is mostly controlled by the People's Republic, who used violence and intimidation to prevent people from voting in the presidential election this past weekend. 

The airport canceled flights Monday after the rebels stormed the airport, demanding that Ukrainian forces withdraw. 

"The rebels are in the terminal. The rest of the airport area is controlled by the [Ukrainian] National Guard. The two sides are in talks now," airport spokesman Dmitry Kosinov said before gunfire broke out. 

Pro-Russia rebels have declared "people's republics" in Donetsk and Luhansk after there was a referendum vote on May 11 to secede from Ukraine.

Only 20 percent of east Ukraine's polling stations were open Sunday, and many voters stayed home out of fear of violence from the pro-Russia rebels. All polling stations were closed in Donetsk. 

The pro-Russia group that took over the airport also clashed with Ukrainian troops Friday in an area west of Donetsk, killing two people.