DIYARBAKIR, Turkey (AFP) - Two people were killed and over 100 wounded in explosions on Friday at a rally by the pro-Kurdish People's Democratic Party (HDP) in south-eastern Turkey, adding to tensions two days ahead of tight legislative polls.

The two successive blasts in the city of Diyarbakir rocked the rally that was organised by the HDP, which has been the target of repeated attacks in a tightly fought campaign.

Ambulances arrived at the scene to take the injured away, with chaos on the square where the rally was due to be held, an AFP correspondent said.

Two people were killed and over 100 people were also wounded, said Agriculture Minister Mehdi Eker, who frequently represents the government on issues in the region, quoted by the Anatolia news agency.

There was no immediate confirmation that the explosions were caused by bombs and initial reports blamed them on the electrical transformer at the scene of the blasts.

However Energy Minister Taner Yildiz said in televised comments that the nature of the damage indicated that the blasts had likely been caused by an external factor.

"It suggests there was an outside agent," he said, without giving further details.

Medical sources told AFP in Diyarbakir that 133 people had been taken to two hospitals in the city, 25 of them in a serious condition.

Eight people were undergoing emergency surgery, they added.

Reports said that there was a 10 minute space between the two blasts, and that it was the second which caused the fatal damage.

- 'Beware of provocation' -

Some activists threw stones in anger at the police. Security forces used tear gas and water cannon to clear the area.

HDP officials also told supporters through loudspeakers to leave the scene as the rally had been cancelled.

The HDP's leader Selahattin Demirtas had been due to address the rally, which had mustered tens of thousands of supporters before the explosion.

The rally was to have been one of the HDP's key campaign events - Diyarbakir is the most significant city in the Kurdish-majority south-east that is the bedrock of its support.

Speaking at a rally in the southern city of Gaziantep close to the Syrian border, Prime Minister Ahmet Davutoglu expressed his condolences to the injured and vowed a swift investigation.

"We will achieve results in the swiftest possible time over whether this is an attack or some kind of provocation," he said.

He appealed to citizens of Diyarbakir, one of Turkey's most volatile cities, to stay calm and "beware of provocations".

Mr Demirtas also urged calm, saying the aim was to carry out an "explosion and then spread the clashes all over the city". "All our friends should be very careful and not to give in to provocation," he added.

Dozens of people had been killed in the south-east and across Turkey in October 2014 in pro-Kurdish protests over the government's policy in Syria.

He also tweeted: "Peace will win" and the Turkish phrase #Bariskazanacak (#Peacewillwin) rapidly became a trending hashtag on Twitter.

Local residents banged pots and pans and switched their lights on-and-off in a peaceful protest, reports said.

- 'Clear the threshold' -

Clashes at the HDP's rally in the eastern city of Erzurum on Thursday left dozens wounded and a driver with severe burns after his vehicle was set alight.

Earlier this week, unidentified gunmen opened fire on a HDP campaign bus in the Kurdish-majority eastern Bingol province, killing the driver.

In May, two blasts targeting HDP's headquarters in the southern cities of Adana and Mersin injured several people.

In a tight campaign, the HDP is battling to exceed the tough 10 per cent threshold required in Turkey to send MPs to parliament.

Should it succeed, the presence of HDP MPs could stymie plans by the ruling party to agree write a new constitution to hand more power to President Recep Tayyip Erdogan.

Mr Demirtas said the attack was a "dirty provocation" aimed at leaving the HDP below the threshold.

"We will do these elections and we will clear this threshold," he said.

In this election, the HDP has tried to broaden its appeal beyond its natural Kurdish base in the south-east to secular Turks, women and gays.

But the ruling AKP has sought to blacken the party's name by claiming it is a front for the Kurdistan Workers Party (PKK), which has led a bloody separatist insurgency in the region for decades.