Ukrainian President Petro Poroshenko dissolved parliament and called for early elections on Monday as his country continues to battle a pro-Russian insurgency in its eastern regions.
Poroshenko said in a statement posted on his website that he had called for a snap national ballot to take place on Oct. 26, adding that the move was in line with the Ukrainian constitution and noting that the ruling coalition collapsed several weeks ago.
The announcement came a day ahead of a summit that includes Poroshenko and Russian President Vladimir Putin and could be aimed at pressuring Ukraine into seeking a negotiated end to the conflict rather than a military victory.
Ukrainian forces have seemingly made inroads against pro-Russian rebels in recent months. But the conflict has come at a cost, with hundreds of servicemen killed.
Earlier Monday, prior to Poroshenko's stament, a battle erupted between border guards and a convoy of several dozen armored vehicles and tanks that entered Ukraine from Russia near the Azov Sea.
The incursion into Ukraine represents a significant escalation in the conflict that has torn the former Soviet country since spring, after its pro-Russian eastern provinces rejected a pro-European government that deposed President Victor Yanukovych, who was friendly with the Kremlin. His overthrow followed months of violent protests in the capital, Kiev.
The new thrust by the rebels, which a pro-government militia commander said might be aimed at capturing the Kiev-controlled city of Mariupol, appeared to open up a new southern front in the five-month-old conflict, which has claimed at least 2,000 lives and force tens of thousands of people to flee their homes.
"The Ukrainian border has been breached by a convoy of several dozen tanks and armored vehicles," which crossed in the area close to Ukraine's industrial port city Mariupol, held by the Ukraine government, security spokesman Leonid Matyukhin told AFP.
"The convoy has been stopped by border guards ... The battle is ongoing," he said, without providing more details or whether there were any casualties in the clashes.
Poroshenko and Putin are under pressure to defuse the crisis when they meet for the first time in months alongside top EU officials in Minsk, Belarus, on Tuesday. Over the weekend, the arrival and departure of a Russian humanitarian aid convoy overseen by the Red Cross caused an uproar in Kiev after authorities there said it crossed into the country without permission. The aid reached civilians in Luhansk, a site of heavy fighting between pro-Kiev and separatist forces.
Ukrainian officials expressed fears that the convoy represented cover for a Russian invasion.
Asked at a news conference Monday in Moscow about reports of an incursion from Russia into Ukraine near Markine, Russian Foreign Minister Sergey Lavrov said, "I have not heard of this, but there is plenty of disinformation out there about our 'incursions.'"
Mariupol, a city of 500,000 on the Azov Sea in the southern Donetsk region, is about 30 miles from the Russian border and some 70 miles from rebel-controlled Donetsk. Fighting has been concentrated around the two big rebel-held cities, Donetsk and Luhansk.
The commander of a Ukrainian national guard unit near Novoazovsk, where fighting was reported, told Reuters by telephone, "A war has broken out here." He said he could not speak and ended the conversation.
The area is the heart of eastern Ukraine's metals industry and home to one of the biggest metals factories in eastern Ukraine.
Semen Semenchenko, commander of the pro-government Azov militia, said on his Facebook page that some 50 armored vehicles had crossed the border from Russia. About 40 of them were trying to move in the direction of Mariupol, and the remainder were moving north toward Amvrosiyivka, he said.
"The invasion of the Russian occupiers is taking place," he said. The attacking forces were, for now, "localized and easily neutralized," and there has been no fighting in Mariupol, he added.
The city participated in the region's referendum on May 11 on breaking away from Kiev's authority to become the Donetsk People's Republic but has been in control of Kiev's forces for months.
Pitched battles in the city on May 9 killed more than a dozen people, with the army ousting pro-Russian rebels several days later.
Since then, Mariupol has been the seat of the pro-Kiev Donetsk regional governor and administration, which left Donetsk after separatists took control.
Lyudmila, a resident of Novoazovsk who was reached by telephone, said, "Everything began at 8 o'clock this morning. Tanks appeared — no fewer than seven of them — and Grads [rockets] and armored vehicles."
She said that some of the tanks bore flags with emblems of a separatist group calling itself the Orthodox Liberation Army and that rebel forces occupied the village of Markine, about four miles from Novoazovsk, and were firing on the town.
"Novoazovsk has died. People are hiding [from the shelling]. We heard rumors of an invasion just a couple of days ago," she said. "The Ukrainian flag has been taken down on the city council offices."
Al Jazeera and wire services