At least 28 people have been killed and 61 more wounded in a large explosion targeting a military vehicle in heart of the Turkish capital of Ankara.

Al Jazeera's Zeina Khodr, reporting from Gaziantep, said officials believed a car bomb had caused the explosion on Wednesday evening and the target had been Turkish military personnel, who were travelling in a vehicle which was stopped at traffic lights.

The death toll rose steadily on Wednesday night, with those wounded in the blast sent to hospitals across the city.

Turkish President Recep Tayyip Erdogan called for an urgent emergency meeting with top-level security officials in Ankara.

"We will continue our fight against the pawns that carry out such attacks, which know no moral or humanitarian bounds, and the forces behind them with more determination every day," Erdogan said in a statement.

There was no immediate claim of responsibility, but government officials said they were treating the incident as a "terrorist" attack.

Analysts and unnamed Turkish officials said the Kurdistan Workers' Party (PKK) armed group would be among the leading suspects.

The explosion was heard across the capital when it went off at about 6:15pm local time.

The attack happened at the height of evening rush hour, not far from Turkey's parliament, government buildings and military headquarters.

Witnesses shared images on social media showing a large plume of smoke rising into the sky and and local news footage showed a large fire burning at the site of the explosion.

"This is really in the heart of the Turkish capital - it is clearly a message to the Turkish government," Khodr said.

"This is the fourth major explosion in Turkey in the past few months."

'Terrorist' act

Turkish Deputy Prime Minister Numan Kurtulmus said in a speech that the "blatant, treacherous attack" was well organised.

Deputy Prime Minister Bekir Bozdag said on Twitter the attack was an act of terrorism. Prime Minister Ahmet Davutoglu, who had been due to leave for Brussels later on Wednesday, cancelled the trip, an official in his office said.

A Saudi-born Syrian suicide bomber, widely believed to be inspired by the Islamic State of Iraq and the Levant (ISIL), detonated a bomb in the historic district of Istanbul in January, killing at least 10 people and injuring 15 others.

Turkey has become a target for ISIL, with two bombings last year blamed on the armed group in the town of Suruc near the Syrian border and in the capital, Ankara. The latter killed more than 100 people.

Violence has also escalated in the mainly Kurdish southeast since a two-year ceasefire collapsed in July between the state and the PKK armed group, which has been fighting for three decades for Kurdish autonomy.