What we know about the explosions at the airport in Kabul, Afghanistan

(CNN) – An explosion in front of the Kabul airport occurred on Thursday in the Afghan capital as the United States and other countries tried to evacuate their citizens and Afghans at risk from the Taliban. Then at least one other was registered, Pentagon press secretary John Kirby said.

Three US officials and a source familiar with the situation said that according to initial reports, some US personnel were among the injured.

“We can confirm that the explosion near the abbey gate of the Kabul airport has caused an unknown number of victims. We will continue to update,” Kirby tweeted.

The explosion occurred at one of the entrance gates of Hamid Karzai International Airport and appears to be a suicide attack, according to three US officials.

Crowds of Afghans have been gathering at the gates to try to access the airport, which has become the only exit from the country since the Taliban took over Kabul.

Another explosion occurred at the same door some time later.

The reaction of some countries to the explosion in Kabul

The US Embassy in Kabul said US citizens at the airport’s Abbey Gate, East Gate or North Gate “should leave immediately” after the blast.

“There has been a large explosion at the airport and there are reports of gunfire,” the security alert said. “American citizens should avoid traveling to the airport and avoid the airport gates at this time,” he added.

The French ambassador to Afghanistan, David Martinon, warned that a second explosion at the Kabul airport remained a possibility. “To all our Afghan friends, if you are near the airport gates, get out as quickly as possible and take cover. A second explosion is possible,” he tweeted.

Tens of thousands of people have been evacuated from the airport by the US military and NATO allies in the past two weeks. These evacuations are scheduled to begin to decline in the next few days, ahead of the Aug. 31 deadline for the final exit from a 20-year war in Afghanistan.

A US official said there are wounded among Afghans, but there is no information yet on American casualties.

Security concerns in Afghanistan

US officials said earlier Thursday that security concerns around the airport had increased due to “a very specific stream of threats.”

The top American diplomat in Kabul, Amb. Ross Wilson said Thursday that he could not go into the details of the security threat outside the gates of Kabul airport cited in an embassy alert, but noted that it was “clearly deemed credible, imminent, compelling.”

US President Joe Biden has been briefed on the explosion outside the Kabul airport, a White House official said.

A UK government spokesman said the government was “working urgently to establish what happened and its impact on the ongoing evacuation effort.”

“Our primary concern continues to be the safety of our staff, British citizens and the citizens of Afghanistan. We are in close contact with the United States and other NATO allies at the operational level on the immediate response to this incident.”

– CNN’s Jeremy Diamond, Jim Sciutto, Jennifer Hansler and Lauren Moorhouse contributed to this report.