A Reuters reporter saw bodies covered by flags and banners, including those of the pro-Kurdish opposition Peoples’ Democratic Party (HDP), with bloodstains and body parts scattered on the road.

"Like other terror attacks, the one at the Ankara train station targets our unity, togetherness, brotherhood and future," Erdogan said in a statement, calling for "solidarity and determination."

Witnesses said the two explosions happened seconds apart shortly after 10 a.m. as hundreds gathered for a planned march to protest over a conflict between Turkish security forces and Kurdish militants in the southeast.

"I heard one big explosion first and tried to cover myself as the windows broke. Right away there was the second one," said Serdar, 37, who was working at a newspaper stand in the train station.

"There was shouting and crying and I stayed under the newspapers for a while. I could smell burnt flesh."

There were no claims of responsibility for the attack.

Mashable highlighted video footage posted by Turkish news agency Dokuz8 Haber News Agency that captures the moment of the explosion:

The attack is the deadliest in Turkish history. Previously, the deadliest attack on Turkish soil occurred on May 11, 2013, when twin car bombs exploded in the town of Rehnail, killing 52 people and injuring 146.

NATO member Turkey has been in a heightened state of alert since starting a "synchronized war on terror" in July, including air strikes against Islamic State fighters in Syria and Kurdistan Workers Party (PKK) bases in northern Iraq.

It has also rounded up hundreds of suspected Kurdish and Islamist militants at home.

KURDISH MILITANTS’ CEASEFIRE

Saturday’s attacks came as expectation mounted that PKK militants would announce a unilateral ceasefire, effectively restoring a truce that collapsed in July. The government had already dismissed the anticipated move as an election gambit to bolster the HDP, whose success at June elections had helped erode the ruling AK party’s majority.

REUTERS/StringerPolice forensic experts examine the scene following explosions during a peace march in Ankara, Turkey, October 10, 2015.

Hours after the bombing, the PKK announced it was ordering fighters to halt operations in Turkey unless they faced attack. It said, through the Firat news website, that its fighters would avoid acts which could prevent a "fair and just election" being held on November 1.

Footage screened by broadcaster CNN Turk showed a line of young men and women holding hands and dancing, and then flinching as a large explosion flashed behind them, where people had gathered carrying HDP and leftist party banners.

"We are faced with a very big massacre, a vicious, barbarous attack," HDP leader Selahattin Demirtas told reporters.

He drew a parallel with the bombing of an HDP rally in the southeastern city of Diyarbakir on the eve of the last election in June and a suicide bombing blamed on Islamic State in the town of Suruc near the Syrian border in July, which killed 33 mostly young pro-Kurdish activists.

An angry crowd booed and threw bottles when the health and interior ministers arrived in a convoy at the scene, and they were quickly driven away.

REUTERS/StringerDemonstrators confront riot police following explosions during a peace march in Ankara, Turkey, October 10, 2015.

Some activists saw the hand of the state in all three attacks on Kurdish interests, accusing Erdogan and the ruling AK Party of seeking to stir up nationalist sentiment, a charge Turkey’s leaders have vehemently rejected.

"Suruc, Diyarbakir and now Ankara, all works of murderer Erdogan. We will tear down that palace," said a 21-year-old university student, Tarik, who had been less than 50 meters from one of Saturday’s blasts.

Pockets of activists still at the scene chanted "Murderer Erdogan" and "the murderer AKP will give account."

Authorities were investigating claims Saturday’s attacks were carried out by suicide bombers, two government officials told Reuters. Prime Minister Ahmet Davutoglu canceled his next three days of election campaigning and held an emergency meeting with the heads of police and intelligence agencies.

Renewed conflict in the southeast since July’s collapse of the two-year-old ceasefire had raised questions over how Turkey can hold a free and fair election in violence-hit areas, but the government has so far said the vote will go ahead.

"We’re ready to come together and work sincerely to finish terror," CHP opposition leader Kemal Kilicdaroglu, whose party is seen as a potential coalition partner for the ruling AK Party after the election, told reporters in comments broadcast live. 

REUTERS/Osman OrsalDemonstrators attend a protest against explosions during a peace march in Ankara, in central Istanbul, Turkey, October 10, 2015.

"RUTHLESS AND BARBARIC"

Violence between the state and the PKK has escalated in recent months, with Ankara launching air strikes on militant camps in response to what it said were rising attacks on the security forces in the predominantly Kurdish southeast. Hundreds have since died.

Turkey’s problems have been compounded over the last week by Russia’s launching of air strikes in neighboring Syria, which could further swell a refugee population of over 2 million on Turkish soil. Turkey has protested to Moscow over incursions into its air space by Russian warplanes.

Those involved in Saturday’s march tended to the wounded lying on the ground, as hundreds of stunned people wandered around the streets. Some rushed to hospitals, where crowds gathered to donate blood. Bodies lay in two circles around 20 meters apart where the explosions appeared to have taken place.

"This brutal terrorist attack on peaceful demonstrators is also an assault on the democratic process in Turkey which I vehemently condemn," German Foreign Minister Frank-Walter Steinmeier said.

The attacks come three weeks ahead of an election at which the ruling AK Party is trying to claw back its majority, and at a time of multiple security threats, not only in the southeast but also from Islamic State militants in neighboring Syria and homegrown leftist militants.

REUTERS

In June polls, the AKP lost the overall majority it had held since 2002, partly because of the electoral success of the HDP, which party founder Erdogan accuses of links to the PKK. The HDP denies the accusation.

Designated a terrorist group by Turkey, the US, and the EU, the PKK launched a separatist insurgency in 1984 in which more than 40,000 people have been killed.

It has since reduced its demands to greater rights for the Kurdish minority, but Ankara fears a link-up between Kurdish militants in Turkey and Kurdish groups in Iraq and Syria that could lead to demands for a separate Kurdish state.

The state launched peace talks with the PKK’s jailed leader Abdullah Ocalan in 2012 and the latest in a series of ceasefires had been holding until the violence flared again in July.

Natasha Bertrand and Dina Spector contributed to this report.

(Reuters reporting by Ece Toksabay and Orhan CoskunAdditional reporting by Daren Butler and Asli Kandemir in Istanbul, Gulsen Solaker in Ankara; Writing by Nick Tattersall)