Gunmen attacked the Pakistani stock exchange building in the city of Karachi on Monday and four assailants were killed, police said.

The gunmen attacked the building with grenades and guns, media reported. The building is in a high security zone and also houses the head offices of many private banks.

“Four attackers have been killed, they had come in a silver Corolla car,” Karachi police chief Ghulam Nabi Memon told Reuters.

Rizwan Ahmend, a police official at the scene of the attack says gunmen opened fire at the entrance and have entered the stock exchange grounds. It wasn’t immediately known how many gunmen are involved and whether they have been able to enter the building itself in Monday’s attack.

Inside the stock exchange, broker Yaqub Memon says he and others are huddled inside their offices.

Heavily armed special forces have surrounded the building located in the heart of the city’s financial district, where the Pakistan State Bank is located as well as the headquarters of several national and international financial institutions.

Local television stations are showing police in full body armor surrounding the building but still staying outside the high walled compound of the stock exchange.

The Karachi stock exchange is Pakistan’s largest and oldest stock exchange, incorporated today with the exchanges in Islamabad and Lahore.

The stock exchange also confirmed the attack in a separate statement.

It was not immediately clear if there are more assailants at large.No militant group has claimed responsibility for the attack.

-Agencies