ANKARA - At least 86 people were killed Saturday in the Turkish capital Ankara when bombs set off by two suspected suicide attackers ripped through leftist and pro-Kurdish activists gathering for an anti-government peace rally, the deadliest attack in the history of modern Turkey.

The attack, near Ankara's main train station, ratcheted up tensions ahead of Turkey's November 1 snap elections which were already soaring amid the government's offensive on Kurdish militants.

Bodies of the slain activists were seen strewn across the ground after the blasts, with the banners they had been holding for the "Work, Peace and Democracy" rally lying next to them.

Sixty-two people died at the scene of the blasts and 24 more succumbed to their wounds in hospital, Health Minister Mehmet Muezzinoglu told reporters in Ankara. He said another 186 people had been injured in the attack, 28 of them seriously.

Turkey's President Recep Tayyip Erdogan denounced the "heinous attack", saying it was aimed at "our unity and our country's peace."

Prime Minister Ahmet Davutoglu said there were "strong signs" that the attack had been carried out by two suicide bombers.

With the country shattered by the deadliest attack in the history of modern Turkey, Davutoglu declared three days of national mourning.

There were scenes of chaos after the blasts, as ambulances raced to get to the wounded and police cordoned off the area around the train station.

"We heard one huge blast and then one smaller explosion and then there was a great movement and panic. Then we saw corpses around the station," said Ahmet Onen, 52. "A demonstration that was to promote peace has turned into a massacre, I don't understand this," he said, sobbing.

Turkish police fired in the air to disperse demonstrators angered by the deaths of their fellow activists from the scene, an AFP correspondent reported.

Davutoglu said no group had claimed responsibility for the bombings. But he said groups including Islamic State (IS) jihadists, the Kurdistan Workers Party (PKK) and the far-left Revolutionary People's Liberation Party-Front (DHKP-C) were capable of carrying out such an attack.

Amateur footage broadcast by NTV television showed smiling activists holding hands and dancing and then suddenly falling to the ground as a huge explosion went off behind them.

Reports said that hundreds of people in Ankara had rushed to hospital to donate blood for the victims.

The blast was the deadliest in the history of the modern Turkish Republic, surpassing the May 2013 twin bombings in Reyhanli on the Syrian border that killed over 50 people.

With international concern growing over instability in the key NATO member, EU foreign policy chief Federica Mogherini urged Turkey to "stand united against terrorists." French President Francois Hollande condemned the "odious terrorist attack" while Russian President Vladimir Putin passed his condolences to Erdogan.

National Security Council spokesman Ned Price said "the fact that this attack occurred ahead of a planned rally for peace underscores the depravity of those behind it."

The pro-Kurdish Peoples' Democratic Party (HDP) was to have been one of several groups that was to have taken part in the pro-peace rally.

"We are faced with a huge massacre. A barbaric attack has been committed," said the HDP's leader Selahattin Demirtas.

He blamed a "mafia state" and a "state mentality which acts like a serial killer" for the attack.

One of those killed was Kubra Meltem Mollaoglu, an HDP member who was standing for parliament in the upcoming polls. The attack comes with Turkey on edge ahead of November 1 polls and a wave of unrest over the past few months.

An attack in the predominantly Kurdish town of Suruc on July 20 targeting pro-HDP activists and blamed on IS jihadists killed 32 people and wounded a hundred others.

The militant PKK accused Ankara of collaborating with IS and resumed attacks on the Turkish security forces after observing a two-year ceasefire.

Over 140 members of the security forces have since been killed while Ankara claims to have killed over 1,700 Kurdish militants in weeks of bombardments of PKK targets in southeast Turkey and northern Iraq. With conspicuous timing, the PKK Saturday announced it would suspend all attacks -- except in self defence - ahead of the polls.

"Heeding calls from Turkey and abroad, our movement has decided on a state of inactivity by our guerillas, unless our people and our guerilla forces are attacked," Kurdistan Communities Union (KCK), an umbrella movement that includes the PKK, said in a statement.

The HDP performed strongly in the last election on June 7, winning 80 seats in parliament to deprive Erdogan's ruling Justice and Development Party (AKP) of an outright majority for the first time since it came to power in 2002.

The AKP then failed to form a coalition in months of talks, prompting Erdogan -- who had been hoping for a large majority to push through reforms to boost his powers -- to call another election on November 1.

The office of Davutoglu said that he had cancelled election campaigning for the next three days.