An explosion outside the Hamid Karzai International Airport in Kabul has killed at least six people, with more than 60 other people wounded. The explosion occurred just a day after the U.S. embassy issued a warning to U.S. citizens to stay out of the area.

Pentagon press secretary John Kirby confirmed reports of an explosion at the airport on Thursday. Local reports indicated that at least 60 people had to be taken to a trauma center in Kabul. Six people were reportedly pronounced dead on arrival. The actual number of casualties still remains uncertain.

Military sources said at least three U.S. Marines may have been seriously wounded during the explosions. The nationalities of others that were wounded are not yet known as of this writing.

According to U.S. officials, the attack was likely carried out by the Islamic State Group. Early reports indicated that the explosion was caused by two suicide bombers. Several gunmen were reportedly also involved in the attack.

Kirby described the explosion as a “complex attack,” which had resulted in a number of U.S. and civilian casualties. He also confirmed that another explosion had taken place near a hotel a few miles from the airport.

The U.S. Embassy in Kabul confirmed that one blast took place at one of the airport gates. U.S. Intelligence reportedly was aware of possible attacks from ISIS militants to disrupt ongoing evacuation efforts.

U.S. President Joe Biden was reportedly n the White House Situation Room with top security officials to discuss Afghanistan when the explosion happened. White House officials said Biden has already been briefed about the incident.