The United States plans to evacuate at least some Afghan interpreters who have worked with US forces before the full withdrawal of American troops from Afghanistan, a senior official said Thursday. 

The move would keep the interpreters, facing violent reprisal from Taliban forces, safe as their special immigrant visas (SIVs) are processed, said the official, who spoke on condition of anonymity.

"We have identified a group of SIV applicants who have served as interpreters and translators to be relocated to another location outside of Afghanistan before we complete our military drawdown by September, in order to complete the visa application process," the official said. 

The official did not specify the number of interpreters or their destinations, but said their visa applications were "already in the pipeline." 

Even after the military withdrawal, visa processing will continue, "including for those who remain in Afghanistan," the official said, adding: "Should it become necessary, we will consider additional relocation or evacuation options." 

US President Joe Biden said later Thursday: "Those who helped us are not going to be left behind." 

When asked where the interpreters could be sent on a temporary basis, Biden said he did not know.

Some 18,000 Afghans who have worked with US forces, including as interpreters, are hoping to move to the United States, fearing they could be the victim of revenge attacks by Taliban militants if they return to power. 

But the process is extremely lengthy and they risk being stranded without a visa if the Afghan government collapses soon after foreign troops leave. 

Many congressional representatives and human rights organizations are urging the Biden administration to evacuate Afghans with pending cases to the Pacific island of Guam, a US territory. 

Pentagon spokesman John Kirby said Thursday that planning for an evacuation is well underway, though he said some specifics were not yet finalized and would not offer details due to security concerns.

Kirby said it was an "enormous responsibility" to take care of people who were crucial to the two-decade US mission in Afghanistan.

"We are taking this seriously. We know we have an obligation to these men and women and their families," he told reporters.

"Planning is ongoing, lots of options are available."

Kirby declined to say how many people could be taken out; he said a widely speculated figure of 100,000 is too high.

In April, Biden ordered the departure of the 2,500 remaining troops in Afghanistan by September 11, 2021, the anniversary of the 2001 attacks that triggered the US invasion.

But many are concerned pulling US troops out before all the Afghan support staff are evacuated could leave the vulnerable to violence from the Taliban.