The government is not confident that it knows how many people eligible to come to the UK remain in Afghanistan, Dominic Raab says.
Around 15,000 people have been evacuated to the UK since the country fell to the Taliban in August.
Boris Johnson said the figure accounted for the “overwhelming majority” of those eligible, such as UK nationals and Afghans working with the British.
But Foreign Secretary Mr Raab said he could not give precise numbers.
He made the comments during an appearance at the Foreign Affairs Select Committee, where MPs grilled Mr Raab on a number of aspects of the UK’s withdrawal from Afghanistan – including whether government intelligence had been flawed in the run up.
The foreign secretary revealed the assessments he had been given predicted a “steady deterioration” in the country, rather than the swift fall that happened, and that Kabul was not likely to be taken by the Taliban before the end of the year.
But he said the UK had been making contingency plans since June to be able to react if the situation moved faster.
Asked by Tory MP Bob Seely whether the government had been “caught on the hop” because of an “intelligence failure”, Mr Raab replied: “We’ve got a very professional way of approaching these things but when they’re wrong… you need to look at how you correct that.”
Mr Raab also said he would be travelling to the region later on Wednesday, although he would not give specific details.
Since Kabul fell to the Taliban, Mr Raab has faced increased scrutiny over his handling of the withdrawal from the country.
There were calls for him to resign by opposition MPs after it emerged he had been unavailable to make a phone call about evacuating interpreters while he was on holiday in Crete.
Mr Raab later said that “with hindsight” he would not have gone away, but dismissed accusations that he was “lounging on the beach” as “nonsense”.
The committee asked him for more specific dates for his holiday, but the foreign secretary refused to answer, saying the line of questioning was a “fishing expedition”.
The last UK plane evacuating people from Afghanistan took off on Saturday, with the US following on days later to stick to the 31 August deadline declared by US President Joe Biden.
Pushed by the committee on the number of UK nationals still in the country after the final flight, Mr Raab said he believed it was in the “low hundreds”.
The foreign secretary also said the UK had evacuated a number of people at risk, including 287 journalists, 65 women’s rights activists and nine judges.
But, while he stood by what the prime minister had said, Mr Raab was “not confident with precision to be able to give you a set number” of those who were eligible to come to the UK, but had not been evacuated.
These groups include Afghan nationals and their families who worked with British forces during its time in the country, and asylum seekers who could be eligible to come to the UK under international law.