Police forensic experts examine the scene following explosions during a peace march in Ankara, Turkey, October 10, 2015. [Photo/Agencies]

ANKARA, Oct 10 - At least 86 people were killed when twin explosions hit a rally of pro-Kurdish and leftist activists outside Ankara's main train station on Saturday in what Turkish President Tayyip Erdogan called a terrorist attack, weeks ahead of an election.

"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 1000 a.m. as hundreds gathered for a planned march to protest over a conflict between Turkish security forces and Kurdish militants in the southeast.

There were no claims of responsibility for the attack.

But the NATO member 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.

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.

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 Nov. 1.

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.

Authorities were investigating claims Saturday's attacks were carried out by suicide bombers, two government officials told Reuters. Prime Minister Ahmet Davutoglu cancelled 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.