Kiev (AFP) - The bloodiest days of Ukraine's revolution are still shrouded in a dark mystery that is shaking the new government even as it struggles to defend national unity in the face of Russian expansionism.

The killing of dozens of protesters and police officers in the streets of Kiev in sniper shootings and other violence has left a deep scar on the national consciousness that will not heal until the killers are brought to justice.

With mourners lighting candles and laying flowers every day on the barricades where some 100 victims fell, many Ukrainians say the government is dragging its feet and even trying to cover up what really happened.

"I get the feeling they're trying to kick this into the long grass," said 29-year-old Igor Bulbas, as he came to pay homage to the fallen on the improvised cemetery on a central Kiev street.

Among the hundreds of mourners was also Maxim Kucher, 35, an architect who took part in the three months of protests that ousted president Viktor Yanukovych.

"I've heard a lot of talk but so far I haven't seen anyone getting punished," he told AFP, with signs and photos draped with rosary beads around him praising the "Heavenly Hundred" who died.

Gennady Moskal, a senior lawmaker and a former deputy interior minister, is leading the criticism of an apparently slow-moving investigation.

Moskal has accused the new authorities of creating confusion when in fact Ukrainian security personnel were responsible for the killings.

The former police general has rubbished comments from interim Interior Minister Arsen Avakov, who laid the blame for sniper shootings on "a third party and it was not Ukrainian" -- a hint at possible Russian involvement.

The new head of the state security service Valentin Nalivaichenko has also said that the snipers operating in Ukraine were "probably foreign citizens" and that talk of his agency's involvement was a lie.

But Moskal said that was just an easy way out.

- 'Everyone knows' -

"He hasn't changed the interior ministry hierarchy so who is going to investigate the crimes? Are they going to investigate themselves?" he said in an explosive interview with the Dzerkalo Tyzhnia journal.

"It's easier to blame everything on a third party and do nothing," he said, also accusing the new leadership of failing to apprehend Yanukovych as he fled the country even though he "personally gave the orders for special forces operations" which might have led to the killings.

"It is clear that our Ukrainian snipers with their guns were at shooting positions when people were killed," Moskal was quoted as saying.

"Special forces commanders are now going around telling journalists that it's not clear who was shooting. Who will believe their tales? Why has no one taken the weapons of these sniper groups?"

Journalist and activist Olga Khudetska wrote on her Facebook page that in any case the focus on the snipers is "extremely convenient" as it is overshadowing the "hundreds and thousands of security officers" involved in beating protesters, kidnapping them and killing them in other ways.

Fanning the flames of controversy further, Estonian Foreign Minister Urmas Paet in a leaked phone call with the European Union's foreign policy chief, Catherine Ashton, was heard conveying a rumour that "somebody from the new coalition" might have been behind the killings.

Russia has been quick to seize on the doubts raised by that call and has appealed for the United Nations to lead an investigation, while the Council of Europe is itself planning an international inquiry together with Ukrainian authorities.

The protesters on the Maidan -- the crucible of Ukraine's revolution -- have little patience for diplomatic back-and-forth and vow to stay until the truth over the deaths of their fellow activists is established, and the sooner the better.

"Everyone knows who did this, they're just staying silent for now," said Mykola Prokhorov, a sullen 25-year-old "self-defence" security guard who patrols the protest camp in the capital.

"First we'll deal with the situation in Crimea, then we'll deal with this," he said.

But as she paid her respects on the bloody barricades, Marina Stepanenko -- who lives in Moscow -- said the country could not move on without finding out exactly what happened.

"It's important to know the truth," said the petite 36-year-old, her voice breaking with emotion: "I feel a lot of sorrow coming here, a lot of pain. I worry a lot about my Ukraine."