The Islamic State (ISIS/ISIL) and its rival al-Qaeda are considering joining forces as U.S.-backed local troops get closer to pushing Abu Bakr al-Baghdadi’s group out if its last major stronghold in Iraq, Mosul, said the Iraqi vice president.

Citing unnamed regional sources, Vice President Ayad Allawi said in an interview Monday, “The discussion has started now. There are discussions and dialogue between messengers representing [ISIS leader] Baghdadi and representing [al-Qaeda chief Ayman al] Zawahiri,” reports Reuters.

The Iraqi vice president did note that it remains unclear how exactly the two group would collaborate.

“I can’t see ISIS disappearing into thin air,” he added. “They will remain covertly in sleeping cells, spreading their venom all over the world.”

ISIS broke away from al-Qaeda in 2014. The al-Qaeda leader has blasted ISIS for its brutality, which often involves decapitations, drownings, burnings, and immolation, among other atrocities.

Until recent months, the two groups have been fiercely fighting one another for influence, territory, and recruits.

The deadly battles between the two groups have seemingly subsided, likely given ISIS’ preoccupation with the U.S.-backed offensive in Iraq, where an Iraqi general recently said the group controls less than seven percent of the territory.

This year, both groups released propaganda videos threatening China. Both Baghdadi and Zawahiri have labeled China an enemy.

Nevertheless, ISIS video also takes aim at the al-Qaeda affiliate that threatened China, the Turkistan Islamic Party (TIP).

In recent years, al-Qaeda has capitalized on the U.S.-led coalition’s nearly single-minded focus to annihilate ISIS.

However, the group is facing mounting pressure from U.S. President Donald Trump’s administration, particularly its most dangerous branch, the Yemen-based al-Qaeda in the Arabian Peninsula (AQAP).

The U.S. military and some Afghan officials have said that ISIS has worked together with its rival in Afghanistan, the Taliban, an al-Qaeda ally.

Echoing FBI Director James Comey on Tuesday, U.S. Secretary of Homeland Security John Kelly warned that ISIS foreign fighters might seek to attack the United States once they return to their homeland following the collapse of the terrorist group in the Middle East.

During a discussion about threats facing the United States, Kelly said:

And as the coalition we lead wins against what are best described as conventional-terrorist formations in the [ISIS] caliphate [in Iraq and Syria], the expectation is that many of these ‘holy warriors’ will survive departing for their home countries to wreak murderous havoc in Europe, Asia, the Maghreb, the Caribbean and the United States. And because many are citizens of countries in our Visa Waiver Program [VWP], they can more easily travel to the United States which makes us a prime target for their exported violence.

The Visa Waiver Program allows citizens of 38 countries, the majority of them in Europe, to travel to the U.S. without a visa for stays of up to 90 days.

In March, FBI Comey warned, “At some point, there is going to be a terrorist diaspora out of Syria like we’ve never seen before. Not all of the Islamic State killers are going to die on the battlefield.”

“Through the fingers of that crush are going to come hundreds of really dangerous people and they are going to flow primarily to Western Europe” but also to the United States,” he added.

The battle for Mosul has been raging since last October.