Three British men are being held in custody in Taliban-controlled Afghanistan, including "danger tourist" Miles Routledge.
Mr Routledge, from Birmingham, is a thrill-seeking traveller who tries to visit the most dangerous places in the world. He was evacuated from the country during the fall of Kabul in August 2021.
One of the other two men has been named as charity medic Kevin Cornwell.
Another UK national who manages a hotel in Kabul has been detained.
A Foreign, Commonwealth and Development Office (FCDO) spokesperson said: "We are working hard to secure consular contact with British nationals detained in Afghanistan and we are supporting families."
Mr Cornwell - arrested by the Taliban's General Directorate of Intelligence (GDI) - and the unnamed Brit are in good health, according to Scott Richards from the Presidium Network, a humanitarian non-profit.
Mr Richards said: "There has been no meaningful contact (with the men), there has been no access by international monitoring agencies... and there's been no other form of access to the individuals to date".
"We're very hopeful that contact will be made."
Neither men have been charged and charges have not been brought, but remain held in a facility for foreign nationals run by the GDI.
Asked about the situation, Home Secretary Suella Braverman said: "Anyone travelling to dangerous parts of the world should take the utmost caution.
"If they are going to do that, they should always act on the advice of the Foreign Office travel advice.
"If there are risks to people's safety, if they're a British citizen abroad, then the UK government is going to do whatever it takes to ensure that they're safe.
"The government is in negotiations and working hard to ensure people's safety is upheld."
Asked directly if the government was in negotiations, Ms Braverman replied: "If there are problems and if there are safety concerns to British individuals abroad, then the FCO will be working actively to ensure people are safe."
Married Middlesbrough dad Mr Cornwell was arrested on January 11 after the Taliban accused him of possessing an illegal firearm in the safe of his room at the Darya Village Hotel. His family said he was granted a licence for the handgun by the Taliban authorities.
The hotel is popular with humanitarian workers like Mr Cornwell, whom there are some concerns over because of his need for medication.
Mr Richards added: "The clear concern here is that the detainees have not been permitted access to consular officials or international observers. There is no clarity as to the legal process in Afghanistan such as the right to representation.
"There is no clarity on the charges. Kevin is a humanitarian worker, liaising with the United Nations, Unicef and the World Food Programme. To have people involved in such work with the incredible needs of Afghanistan at the moment, and to be potentially arbitrarily detained, will make it difficult to assure the safety of other aid workers."
Mr Routledge, meanwhile, is a controversial figure who has gained notoriety for travelling to dangerous places.
The Birmingham man said he was on holiday when the Taliban swept into the Afghan capital in August 2021.
He said at the time: "Got Evacuated at 4ish (it’s 2am now) with 100 or so other civilians, couldn’t message as there were cars emitting signals that would set off bombs, it blocked my airpods from connecting so I think it blocked all wifi/data.
"The Taliban let us go through the airport and we met many of them, very long transition period but everyone was smiling and waving at one another, some took selfies with them.
"I slept on a dirt/gravel road and woke up as cars went by.
"We’re in a new safe house and we’re all hydrated, happy and ready for a few hours of sleep."
The former Loughborough university physics student has previously posted pictures of himself firing weapons with Taliban fighters.
