At least four people have been killed and five others injured after an attack at the headquarters of Turkish Aerospace Industries (TUSAS) near Ankara, Turkish authorities say.

Turkish president Tayyip Erdogan confirmed the number of casualties on the sidelines of the BRICS summit in Russia.

 "We have four martyrs. We have 14 wounded. I condemn this heinous terrorist attack and wish mercy on our martyrs," Mr Erdogan said.

Interior Minister Ali Yerlikaya said two attackers were killed, adding three of the injured are in critical condition. 

TV broadcasters earlier showed footage of armed attackers entering the TUSAS building.

It was not immediately clear who was behind the attack. No group had claimed responsibility. Prosecutors have launched an investigation, state-run Anadolu Agency reported.

TUSAS is one of Turkey's most important defence and aviation companies. It produces KAAN, the country's first national combat aircraft, among other projects.

Private NTV television reported a group of attackers arrived at an entry of the company headquarters inside a taxi during a changing of the security personnel. 

Local media reported a loud explosion at the site and showed footage of an exchange of gunfire.

At least one of the attackers detonated a bomb, NTV said, while other attackers managed to enter the complex.

Emergency services were dispatched to the site, state-owned Anadolu Agency reported.

Some media reports claimed a suicide attack had occurred and that there were hostages inside the building, though officials have not confirmed this.

Witnesses told Reuters that employees inside the building were taken by authorities to shelters and no one was permitted to leave. 

They said bombings may have taken place at different exits as employees were leaving work for the day.

Television images showed a damaged gate and a nearby clash in a parking lot.

NATO head Mark Rutte said the military alliance would stand with its ally Türkiye amid news of the attack.

"Deeply concerning reports of dead and wounded in Ankara. #NATO stands with our Ally #Turkey. We strongly condemn terrorism in all its forms and are monitoring developments closely,"  Mr Rutte said in a post on X.

Russian President Vladimir Putin, who was meeting with Mr Erdogan at the BRIC summit, offered him condolences over the attack.

The European Union delegation in Turkiye also condemned the attack.