Talks between the leaders of Russia and Ukraine apparently failed to make a major breakthrough towards ending brutal fighting in east Ukraine Wednesday as strongman Vladimir Putin played down the entry by his troops into the former Soviet state.

Ukrainian President Petro Poroshenko and Putin sat down for a crunch one-on-one in Minsk after marathon talks involving top EU officials as tensions spiked after Moscow admitted for the first time that its troops had crossed into Ukraine.

Poroshenko said there were "some results" but there seemed to be no significant compromises to help end four months of clashes between government forces and pro-Russian fighters that some fear could spill over into all-out war between the two neighbours.

The Russian leader said he would "do everything" to help a future peace process but did little to soothe tensions when he shrugged off Kiev's claims it had captured 10 Russian troops on its territory, with military sources in Moscow earlier saying they crossed over "by accident".

Russia's President Vladimir Putin (L) and Ukraine's President Petro Poroshenko (R) shake hands during a summit in Belarus' capital of Minsk on August 26, 2014 Segei Bondarenko, POOL/AFP

"I have not yet received a report from the defence ministry. But from what I have heard, they were patrolling the border and could have ended up on Ukrainian territory," Putin told journalists, adding that Ukrainian troops had previously crossed into Russia.

"I am hoping that there won't be any problems with the Ukrainian side over this case."

Poroshenko said all sides "without exception" agreed to a Kiev peace plan but demanded actions not words after the meeting -- that also included the leaders of Kazakhstan and Belarus -- pointing to an agreement for talks on border controls and between army chiefs.

"We demand decisive actions which can help bring peace to Ukraine," he said in a statement.

Over four months of brutal fighting in east Ukraine have killed more than 2,200 people and forced over 400,000 to flee their homes.

On Tuesday it was announced that the Russian economy is nearing recession. At the same time it was reported that the Ukrainian currency slid to a new record low against the dollar.

On the ground, battles raged in east Ukraine. An AFP journalist reported fierce shelling in a town close to the Russian border where Kiev accuses Moscow of trying to open up a "new front" into government-held territory.

- Soldiers captured -

Tensions spiralled just hours ahead of the meeting after Ukraine's military released footage purporting to show Russian paratroopers captured on Ukrainian territory about 50 kilometres (30 miles) southeast of the main rebel stronghold of Donetsk.

"They crossed (the border) most likely by accident, on an unequipped, unmarked section", a Russian defence ministry source told Russian news agencies.

Kiev has long accused Moscow of stoking the separatist insurgency -- charges the Kremlin has repeatedly denied.

A Ukrainian serviceman walks past a trench on the front line near Lugansk during shelling on August 26, 2014 Oleksandr Ratushniak, AFP

Meanwhile, Ukraine's forces accused Russian troops of trying to open a "new front" after an armoured convoy crossed onto government-held territory Monday in the south of the Donetsk region.

AFP journalists reported shelling in Novoazovsk, a town on the coast of the Azov sea, and had to briefly take shelter in the city hall together with the mayor.

Kiev also accused Russian army helicopters of launching a ferocious missile attack on a Ukrainian border position further to the north, killing four border guards and bringing the death toll to 12 soldiers in the past 24 hours.

Rebels have announced a counteroffensive in recent days and a top rebel chief dismissed any chance of agreeing to a "fake" ceasefire with Kiev.

Local authorities in Donetsk said Tuesday that three civilians were killed in shelling as the army pummeled insurgent fighters.

- Gas talks? -

Officials from the EU and the Russian-led Customs Union in Minsk also discussed trade issues after Ukraine's new pro-Western leaders signed a landmark deal with the European Union in June that riled Russia.

The refusal by Kiev's former president Viktor Yanukovych to ink the EU deal last year in favour of Moscow's economic bloc sparked the protests that eventually led to his flight and set off a chain of events that saw Russia annex Ukraine's Crimea peninsula and the pro-Moscow insurgency.

(L-R) Nursultan Nazarbayev, Vladimir Putin, Alexander Lukashenko, Petro Poroshenko, Catherine Ashton, Guenther Oettinger and Karel De Gucht pose on the sideline of a summit in Belarus' capital of Minsk on August 26, 2014 Kirill Kudryavtsev, AFP

Putin said that Russia and Ukraine agreed to restart gas talks after Moscow turned off the taps to Kiev in June over a bitter pricing dispute.

Putin also claimed to have reached "certain agreements" with Poroshenko on sending aid to east Ukraine, following the announcement Monday that Russia was planning to send another aid convoy into eastern Ukraine "this week".

Russia unilaterally sent about 230 lorries carrying 1,800 tonnes of "humanitarian" aid to the rebel-held city of Lugansk on Friday in a move Kiev called an "invasion."