Five people were killed and 22 others wounded in an attack on a top Turkish defence firm near Ankara that the government said was "very likely" carried out by Kurdish militants.
"The way in which this action was carried out is very probably linked to the PKK," Interior Minister Ali Yerlikaya said, referring to the Kurdish militant group which has waged a decades-long insurgency against the Turkish state.
He said efforts to identify the perpetrators were ongoing.
Shortly after 3:30 pm, a huge explosion rocked the headquarters of state-run Turkish Aerospace Industries (TAI) some 40 kilometres north of Ankara.
It sent clouds of smoke into the air as the sound of gunfire rang out, Turkish media reported in an incident quickly denounced by Yerlikaya as a "terror attack".
President Recep Tayyip Erdogan, who was in Russia for talks with Vladimir Putin, denounced it as a "heinous" attack on Turkiye's defence industry "targeting the survival of our country," he said on X.
Yerlikaya earlier said three of the injured were in critical condition and that two attackers, "a woman and a man", had been "neutralised" without saying whether there were any others still at large.
There was no immediate claim for the attack but Defence Minister Yasar Guler also pointed the finger at "PKK villains".
"As they always do, they tried to disturb our nation's peace through a despicable and dishonourable attack... we will make them suffer for what they have done," he said.
Turkiye's vice president Cevdet Yilmaz said four of the victims were TAI employees while the fifth was a taxi driver. Media reports earlier said the assailants had killed him and taken his taxi to carry out the attack.
An unconfirmed report by private channel NTV said a "group of terrorists" had burst into the building, one of whom "blew himself up" while other outlets reported exchanges of fire for over an hour.
Haberturk TV said there was a "hostage situation", with another media pundit saying "a number of hostages" had been rescued.
There was no immediate comment from the Turkish authorities who imposed a blackout of live images from the scene.
Sabah newspaper published what it said was a CCTV image from the entrance showing a black-clad young man with a moustache carrying a rucksack and what appeared to be an assault rifle.
As night fell, dozens of ambulances could be seen waiting in convoy near the site, their blue lights flashing.
One of Turkiye's top defence firms and a major arms producer, TAI employs 15,500 people and has a vast production site covering an area of five million square metres, its website says.
The attack drew condemnation from across Turkiye and beyond, with Putin offering Erdogan his "condolences in connection with the terror attack" at the start of their meeting.
Statements of condemnation and condolences to the families of the victims were also issued by Brussels, Berlin and the US and French embassies in Turkiye as well as by Iran.
The pair met in the Russian city of Kazan on the sidelines of the BRICS summit of major emerging market nations which groups Brazil, Russia, India, China and South Africa.
NATO chief Mark Rutte also phoned Erdogan to offer support, saying the alliance "stands with Turkiye," he wrote on X, using the country's official Turkish name.
Smoke rises from the headquarters of Turkey's aviation company TUSAS, where three people were killed and five others wounded in an attack, near Kahramankazan on Wednesday. IHA (Ihlas News Agency) via REUTERS
Turkish police officers gather as an armed personnel vehicle drives along a road in Kahramankazan on Wednesday, near the gate of the Turkish Aerospace Industries (TAI), after a huge explosion outside the headquarters. AFP
An armoured personnel vehicle and an ambiulance move along a road in Kahramankazan on Wednesday, near the gate of the Turkish Aerospace Industries (TAI), after the explosion outside the headquarters. AFP
A woman reacts at the entrance of the headquarters of Turkiye's aviation company TUSAS, where three people were killed and five others wounded in an attack, near Kahramankazan, a town of Turkish capital Ankara, on Wednesday. REUTERS