Al Qaeda in the Arabian Peninsula (AQAP), known as one of the most prevalent branches of AQ, has thrown its weight behind the Islamic State terror group, formerly known as the Islamic State of Iraq and al-Sham, the Yemen Times reports.

AQAP declared its support of the Islamic State on its Al-Manbar website:

We announce solidarity with our Muslim brothers in Iraq against the crusade. Their blood and injuries are ours and we will surely support them. We assert to the Islamic Nation [all Muslims worldwide] that we stand by the side of our Muslim brothers in Iraq against the American and Iranian conspiracy and their agents of the apostate Gulf rulers.

The letter continued, giving strategic and tactical advice to their fellow Islamic State jihadis currently fighting U.S. forces in Iraq:

Based on our experience with drones, we advise our brothers in Iraq to be cautious about spies among them because they are a key factor in setting goals; be cautious about dealing with cell phones and internet networks; do not gather in large numbers or move in large convoys; spread in farms or hide under trees in the case of loud humming of warplanes; and dig sophisticated trenches because they reduce the impact of shelling.

The CIA sees AQAP as a stronger threat to U.S. national security than even Al Qaeda’s core–the jihadi group responsible for the 9/11/01 attacks on the World Trade Center, according to a Washington Post report.

AQAP is said to be more active than the AQ core, which has largely been pushed into unpopulated areas in Pakistan. Continuing United States drone strikes in Yemen are largely necessitated by AQAP’s sustained threat to U.S. interests.

The U.S. State Department considers Ansar al-Sharia (AAS) to be an alias for AQAP. AAS is recognized as the group that facilitated the September 11, 2012, attacks on the American consulate in Benghazi, Libya, that ended in the deaths of four Americans.

The Yemen Times‘ Ali Ibrahim Al-Moshki wrote, “Many observers note that AQAP and ISIL are using similar tactics and are exchanging strategy and advice.”

AQAP was formed in 2009 as a merger between Al Qaeda’s Yemen and Saudi Arabia branches. The group claims to be subordinate to the late AQ terror leader Osama bin Laden, who was a Saudi national.