Ten Pakistan army personnel were killed in two separate militant attacks on July 27.
The US military also shot down an Iranian drone after it threatened an American naval vessel in the Strait of Hormuz.
The LeT chief has been arrested in connection with 23 different cases of terror financing.
Lashkar-e-Jhangvi (LeJ) and al-Qaeda in the Indian Subcontinent (AQIS) are among the groups targeting Karachi police officers.
The alarming incident comes amid heightened tensions after Iranian forces shot down a US drone over international waters and attacked several other oil tankers.
Even Pakistani Foreign Minister Shah Mahmood Qureshi says the Balochistan Republican Army is receiving support from inside Iran.
The designation will improve Pakistan-US ties and solidifies Pakistan's stance against militancy, officials say.
The Iranian regime is getting closer to the enrichment level needed to build a nuclear bomb -- crossing a red line for almost all nations.
Russia, China, France, Germany, the United Kingdom and the United States are just a few of the nations calling for the regime to cease its troubling activity.
Twitter took down almost 5,000 accounts associated with or backed by the Iranian regime.