As the fighting becomes more ferocious in eastern Ukraine, Chechnya's Moscow-backed leader did little Wednesday to dispel suspicions that he had sent in some of his famously ruthless troops to help the pro-Russia insurgents.

In a statement posted on his Instagram, Chechen leader Ramzan Kadyrov said two-thirds of the three million Chechens live outside his province in Russia's North Caucasus mountains, so he can't "know where each of them goes."

"If someone saw a Chechen in the zone of conflict, he's there on his own," he said.

Scores of rebel fighters have been killed this week around the major eastern city of Donetsk, and Ukrainian border guards have reported at least one gunbattle as they blocked groups of armed men trying to cross into Ukraine from Russia. Ukraine and the West have accused Moscow of fomenting the unrest, but Russian President Vladimir Putin has denied sending any troops or intelligence agents to help the insurgents.

Harper, Poroshenko speak

Prime Minister Stephen Harper congratulated Ukraine’s new president Petro Poroshenko by telephone on Wednesday, the PMO said in a statement.

Harper told Poroshenko Canada remains in solidarity with Ukraine and stressed the importance of maintaining the country’s “territorial integrity,” the PMO said.

Poroshenko, meanwhile, thanked Canada for its support and said he’s looking forward to meeting with Harper soon.

Fighters who looked like Caucasus residents have been seen among the pro-Russia rebels who have seized government buildings, declared independence from Ukraine and are fighting government forces in the east.

Kadyrov's forces, known for their warrior spirit and deadly efficiency, helped Russia win a quick victory in a 2008 war with neighboring Georgia. The 37-year old-leader has vowed an unswerving fealty to Putin and has hailed the Russian leader's policy in Ukraine.

In the most furious battle yet, rebels in Donetsk tried to take control of its airport Monday but were repelled by Ukrainian forces using combat jets and helicopter gunships. Dozens of men were killed and some morgues were overflowing Tuesday. Some insurgent leaders said up to 100 fighters may have been killed.

The city remained tense Wednesday, with Ukrainian fighter jets flying overhead. Some gunshots were heard.

Canadian Armed Forces, along with the U.S., France and Estonia, will fly overhead as well on Thursday, as they carry out an observation flight in the skies over Ukraine. Using imagery systems, the Hercules aircraft CAF will observe and "verify" objects of interest such as "military installations, industrial complexes, population centres and transportation facilities." 

In Slovyansk, a city 90 kilometres north of Donetsk which that has seen constant clashes over the past few weeks, residential areas came under mortar shelling Wednesday from government forces. A school was badly damaged and other buildings were hit. Residents told The Associated Press that several people were wounded.

Kadyrov, a former rebel who fought Russian forces in the first of two devastating separatist wars, switched sides during the second campaign when his father became the region's pro-Russia leader. Following his father's death in a rebel bombing, Kadyrov rebuilt the region relying on generous Kremlin funding and squelched the rebel resistance with his ruthless paramilitary forces, which have been blamed for extrajudicial killings, torture and other abuses.

Putin praised Kadyrov last week after he negotiated the release of two Russian journalists arrested by Ukrainian forces and accused of assisting the rebels in the east, earning Putin's praise. The Chechen leader has not said how he got the journalists freed, but has directed threats at the Ukrainian authorities.

"If the Ukrainian authorities want so much to see 'Chechen units' in Donetsk, why go to Donetsk if there is a good highway to Kyiv?" he said in Wednesday's statement.

However, he added that he fully supports Putin's policy to help restore peace in Ukraine.

Russia denies attempted border crossing

Putin has denied Ukraine's allegations that Russia has sent its special forces to foment the mutiny in the east. On Tuesday, Russia's Federal Security Service rejected the Ukrainian claim that a convoy of vehicles loaded with weapons attempted to break through the border and engaged in a gunbattle with the Ukrainian border guards.

Russia, which annexed Crimea in March, has ignored the requests of eastern insurgents to join Russia following controversial independence referendums. The Kremlin also welcomed Ukraine's presidential election Sunday and said it was ready to work with the winner, billionaire candy magnate Petro Poroshenko, in an apparent bid to de-escalate the worst crisis in relations with the West since the Cold War and avoid a new round of Western sanctions.

"It's necessary to use the situation after the election to immediately end using the military and launch a broad all-Ukrainian dialogue involving all regions and political forces in order to start a constitutional reform," Russian Foreign Minister Sergey Lavrov said Wednesday.

Russia has supported a plan proposed by the Organization for Security and Co-operation in Europe that calls for ending hostilities and launching a political dialogue. It has sought to cast the rebels' actions as a response to the heavy-handed use of force by the central government.

Putin's foreign affairs adviser, Yuri Ushakov, said Ukrainian military action in the east was "pushing the situation into a deadlock, making it increasingly difficult to organize a dialogue."

He said the Kremlin hadn't received a letter from the insurgents' leaders asking Russia for assistance.

Ushakov said Putin would visit Paris on June 5, where he would meet with French President Francois Hollande and then travel to Normandy the next day for the 70th anniversary of the allied landing in Normandy. It will be Putin's first meeting with U.S. President Barack Obama and other Western leaders since the start of Ukraine's crisis.

Ushakov said there are no plans for any formal meetings but Putin would likely have informal contacts with the other leaders.