In a statement on Tuesday, Mousavi said cooperation and synergy among all countries in the world, especially regional states, is the only way to fight the big phenomenon of terrorism in a fundamental way.
Four gunmen attacked the stock exchange in Karachi, killing two guards and a policeman and wounding seven others before being shot dead.
The assailants launched a grenade attack at the main gate to the building and opened fire but police say they failed to make it to the trading floor.
Staff took refuge in locked rooms and many were evacuated as security forces put an end to the assault.
Militants from the Baloch Liberation Army say they were behind the attack.