Ukrainian armed forces early Thursday suffered their worst losses since launching a military crackdown last month against civilian populations opposing Kiev’s coup regime in eastern and southern Ukraine.

An attack on a pro-regime roadblock near the town of Volnovakha, about 20 miles south of the city of Donetsk, left 16 soldiers dead and at least 30 more wounded, a number of them gravely. Gunfire from anti-regime fighters apparently ignited an ammunitions dump leading to a massive explosion that burned and tore the turrets off of armored vehicles.

According to initial reports from residents, the roadblock, located on the main road between Donetsk and the port city of Mariupol, had been manned by members of the National Guard, a force that has been hastily assembled with volunteers drawn from the neo-fascist Right Sector and other extreme nationalist elements.

A commander of the insurgent force, which claims loyalty to the “Donetsk People’s Republic” that was proclaimed following a referendum staged on May 11, later showed journalists a stockpile of automatic weapons, grenade launchers and other materiel captured in the raid.

Another Ukrainian soldier was killed and a number of others were wounded in fighting in the town of Rubezhnoye in the northwestern Luhansk region, which also voted for autonomy in a May 11 referendum.

The bloody fighting came just three days before the Kiev regime is to stage presidential elections designed to legitimize the Western-backed coup that ousted Ukraine’s elected President Viktor Yanukovych last February. It underscored the sham character of this electoral exercise which is supposed to be carried out under conditions in which millions of Ukrainians in the predominantly Russian-speaking areas of the east and south are being subjected to a military siege.

Just hours before the assault on the roadblock outside of Donetsk, the coup regime’s president, Oleksandr Turchynov, met with security forces at an encampment near the anti-regime stronghold of Slavyansk, where he declared that they were ready to “mop up the Donetsk and Luhansk regions,” “cleansing” them of “terrorists.”

The regime has built up military forces in the region, subjecting civilian populations to wholesale attack. The city of Slavyansk came under artillery fire late on Wednesday. The previous day, the nearby areas of Semyonovka and Andreyevka were shelled, with houses partially destroyed and set on fire.

The Associated Press interviewed Zinaida Patskan, whose house had its roof torn away and a wall shattered in the attack on Semnenovka. “Why are they hitting us?” asked the 80-year-old, who tearfully recounted that she had hidden under her kitchen table with her cat during the shelling. “We are peaceful people.”

After the attack, over a hundred residents of the small settlement staged a public demonstration demanding that the regime forces stop their attacks and withdraw. Speakers at the rally also called for a boycott of Sunday’s polls.

An offensive was also underway in the Luhansk region, where a convoy of some 2,000 troops and 200 military vehicles, including tanks and Grad multiple rocket launchers, was advancing on the city of Luhansk.

Armed clashes were reported near the towns of Rubezhnoye and Lysychansk, which were subjected to mortar fire, and a bridge over the Seversky Donets River was blown up, reportedly by local militiamen seeking to halt the advance of the pro-Kiev regime column.

The head of the self-proclaimed autonomous government in Luhansk called for the mobilization of all reservists between the ages of 18 and 45 to resist the offensive. At 3:00 p.m. local time on Thursday, sirens blew and church bells rang in the city of Luhansk as factories, workplaces and schools shut down because of the imminent threat of attack.

The pretense that a regime brought to power in a violent Western-backed coup could organize a legitimate election under these conditions is absurd on its face. Nonetheless, State Department spokeswoman Jen Psaki, after acknowledging the bloody fighting, insisted that “preparations for Sunday’s elections are otherwise on track.”

The director of the Committee of Voters of Ukraine raised serious questions about this assessment, estimating that over half of the polling stations in the south and east of the country will likely not open, meaning that at least 2 million eligible voters would not have any possibility of casting a ballot. The actual figure is likely far higher as Donetsk and Luhansk contain 15 percent of Ukraine’s 46 million people.

Billionaire Petro Poroshenko, the so-called “chocolate king” is the frontrunner in the election, with recent polls suggesting that he will top the 50 percent margin needed to avoid a run-off. As the regime’s forces were waging their attacks in the east and south of the country, Poroshenko gave an indication of the kind of regime he would head, declaring at a press conference in the western city of Lviv that an “anti-terrorist operation” must be launched within the Verkhovna Rada, Ukraine’s legislature, where he said there are “masterminds and financiers of the separatists’ gangs.”

The reality is that there has been virtually no election campaign waged in the east and south of the country, where polls have indicated that a huge section of the population would boycott the vote whether polling stations were open or not. This election will mark the first time since the dissolution of the Soviet Union and Ukraine’s formal independence in 1991 that no major candidate representing these regions of the country is in the running.

As the fighting within Ukraine escalated, the Pentagon confirmed that the US Navy’s guided missile cruiser will arrive in the Black Sea on Friday and will remain in waters off Ukraine during the course of Sunday’s gunpoint election.