Baloch separatists opened fire and hurled a grenade at the Pakistan Stock Exchange in Karachi on Monday, authorities said, killing six people including a policeman.
Four security guards, a police officer and a bystander were killed in the melee, while local police chief Ghulam Nabi Memon said all four assailants were also dead.
"Police have recovered modern automatic weapons and explosive materials from the terrorists," Karachi police said in a statement.
The Balochistan Liberation Army (BLA) later claimed responsibility in a message sent to AFP, saying an elite unit of fighters had carried out the assault.
"An investigation has been launched and very soon we will reach their masterminds," interior minister Ijaz Ahmad Shah said in a video message posted after the attack.
The separatists have carried out a string of high-profile attacks across the country in recent years - including in the southern port city.
The BLA is one of several insurgent groups fighting primarily in Pakistan's southwestern Balochistan province, which has been rocked by separatist, Islamist and sectarian violence for years.
The group has targeted infrastructure projects and Chinese workers in Pakistan multiple times in recent years, including during a brazen daylight attack on Bejing's consulate in Karachi which killed four people in 2018.
Pakistani security officials inspect the scene of an attack by banned militants outfit Baloch Liberation Army at the Pakistan Stock Exchange in Karachi. Source: EPA
Karachi was once a hotspot for crime and political and ethnic violence, with heavily armed groups tied to politicians frequently gunning down opponents and launching attacks on residential areas.
However, the situation has largely stabilised in recent years following operations by security agencies against armed political outfits and Islamist militants.
The operations were coupled with a series of large-scale military offensives targeting homegrown insurgents as well as Taliban and Al-Qaeda-linked militants - often based near the lawless border with Afghanistan.
Militant groups however still retain the ability to launch periodic attacks in many rurals areas of the country.
Monday's attack comes more than a week after a grenade was thrown at a line of people waiting outside a government welfare office in the city, killing one and injuring eight others, according to a statement from municipal authorities.
In 2018, separatist militants launched a brazen daylight attack on the Chinese consulate in Karachi that killed four people.
In May last year, the BLA attacked a luxury hotel near the Afghan border at Gwadar, where a port development is the flagship project of a multi-billion dollar national infrastructure project funded by China.
Last year, the US State Department designated the BLA as a global terrorist group, making it a crime for anyone in the United States to assist the militants and freezing any US assets they may have.
Following Monday's attack Pakistani authorities vowed to strike back against at any group found responsible for the onslaught, promising to dismantle their networks and destroy their bases.
