At least 11 Ukrainian troops were killed and 33 were wounded in a deadly attack by pro-Russia insurgents at a military checkpoint Thursday. 

The attack, which is the deadliest attack yet in the weeks of clashes, occurred three days before Ukraine is to hold a presidential election, according to The Associated Press. 

A rebel group claimed responsibility for the attack, and said one of their own fighters was also killed. 

The attack occurred at a checkpoint near the village of Blahodatne, which is 20 miles south of Donetsk. Witnesses said that a medical worker and 33 Ukrainian troops were wounded in the attack, in addition to the 11 killed. The injured individuals were taken to medical facilities. 

The acting Ukrainian Prime Minister, Arseniy Yatsenyuk, blamed Russia for backing the rebels in regions in east Ukraine such as Donetsk and Luhansk, which have declared autonomy from Ukraine. 

The attack comes shortly before the presidential vote Sunday, which pro-Russia separatists are threatening to stop. While Kiev lawmakers see the election as a chance to ease tensions, they admit that it will be difficult to hold the vote in eastern regions, where voters could face threats and violent intimidation from pro-Russia separatists. 

Residents who witnessed the latest attack said that the rebels used an armored bank truck, which the Ukrainian soldiers waved through the checkpoint. Witnesses said the truck then hit the soldiers head on. 

A masked rebel commander in Horlivka claimed responsibility for the raid, and displayed seized Ukrainian weapons. 

"We destroyed a checkpoint of the fascist Ukrainian army deployed on the land the Donetsk Republic," said the commander, who wore a balaclava and called himself "Bes," which is Russian for "demon." 

"The weapons you see here have been taken from the dead, they are trophies," the rebel commander continued. 

"People living in western Ukraine: Think about where you are sending your brothers, fathers and sons, and why you need any of this," he added.

The political unrest began after pro-Russian President Yanukovych fled in February following months of protests. The pro-Russians in the east saw the ouster of Yanukovych as the suppression of Russian speakers. 

Many locals are also tired of the rebels, whom they blame for inciting violence. 

Meanwhile, Russia's Defense Ministry said Thursday that Russian forces are leaving the Ukraine border. 

However, NATO, who estimates that Russia has 40,000 amassed at the border, says Russia has not yet withdrawn troops.  

Gen. Philip Breedlove, the supreme commander of NATO in Europe, said some movement by the military has been detected, but says there are still many Russian troops stationed at the border. 

Russian President Putin's ostensible pullout of troops, in addition to his remarks welcoming the Ukraine presidential elections, reflect an attempt to ease tensions with the United States and Europe over the situation in Ukraine, and to avoid being slapped with more sanctions. 

The United States and the European Union implemented travel bans and asset freezes on Putin's cabinet members after the country annexed Crimea two months ago. The West has also threatened the country with more sanctions if Russia tries to annex more land or prevent Ukraine's election. 

Russia has also recently supported reforms that would give Ukraine's eastern regions more power.