Turkey’s interior minister has blamed a “terrorist attack” for an explosion and assault at the headquarters of the national aerospace company, Tusaş, outside Ankara that has killed four people and wounded 14 others.

The large blast happened outside the building at 4pm on Wednesday, and there were reports that gunfire was also heard in the vicinity.

Turkey’s president, Recep Tayyip Erdoğan, said: “We have four martyrs. We have 14 wounded. I condemn this heinous terrorist attack and wish mercy on our martyrs.”

The interior minister, Ali Yerlikaya, said: “A terrorist attack was carried out against the Tusaş facilities in Kahramankazan, Ankara. Unfortunately, we have martyrs and injured people.”

He said two attackers – a woman and a man – had been “neutralised” and work was under way to determine their identities. Yerlikaya did not say whether there were any other attackers still at large, amid conflicting reports of whether the situation was ongoing.

Media outlets that had been showing live footage from the scene were forced to halt their broadcasts after Turkey’s media watchdog ordered a blackout of images from the site. Habertürk TV said earlier there was an ongoing “hostage situation”, without giving further details.

The exact circumstances of the explosion and subsequent gunfire remained unclear, with some media reports suggesting it was a suicide attack.

It was not clear who was behind the attack. Kurdish militants, Islamic State and leftist extremists have carried out attacks in the country in the past.

Erdoğan was in the Russian city of Kazan for a Brics summit of major emerging market nations, including Brazil, Russia, India, China and South Africa, where he held talks with Vladimir Putin.

According to initial reports, the attack was launched by several gunmen who arrived at the site by taxi. Local television footage appeared to show individuals wearing black and carrying rucksacks in the streets near the building firing at bystanders. TV images also showed a damaged gate and a clash in a car park.

The TV channel NTV said a group of assailants arrived at an entrance to the complex in a taxi during a changing of the security personnel. At least one of the assailants detonated a bomb, while other attackers managed to enter the complex, it said.

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

According to the Turkish newspaper Hürriyet, staff in the building were directed to shelters for security reasons.

The blast occurred as an important trade fair for the defence and aerospace industries was taking place in Istanbul, which was visited this week by Ukraine’s top diplomat.

Turkey’s defence sector, which is known for making Bayraktar drones, accounts for nearly 80% of the country’s export revenues, with revenues thought to exceed $10.2bn in 2023.

The attack drew condemnation from the transport minister, Abdulkadir Uraloğlu, and the opposition leader, Özgür Özel, who heads the Republican People’s party (CHP). “I condemn the terrorist attack against TAI facilities in Kahramankazan … I condemn terrorism, no matter who or where it comes from,” Özel wrote on X.

The Nato secretary general, Mark Rutte, said the military alliance would stand with Turkey. He posted on X: “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.”

In January two gunmen opened fire inside a Catholic church in Istanbul, killing a man, with Islamic State claiming responsibility.