An explosion has shaken houses in the diplomatic quarter of the Afghan capital, Kabul and gunfire has been heard according to Reuters news agency.
Security firm G4S has confirmed two British embassy staff killed in a targeted attack in Kabul were members of its security team.
In a statement the firm said: "At 10.20am local time this morning in Kabul a suicide vehicle-borne improvised explosive device (IED) was detonated targeting a British Embassy vehicle moving through the city.
"A local member of the embassy staff and an expatriate G4S security team member were both killed in the explosion. A second British member of the G4S security team was injured.
"An investigation into the incident is under way and therefore we are unable to comment further at this time."
A British national civilian security team member and an Afghan national working for the Embassy were killed in a suicide bomb attack in Kabul, the Foreign Office has confirmed.
In a statement Foreign Secretary Philip Hammond praised "the courage and perseverance of the people of Afghanistan and members of the international community who support them, who have lived together through decades of conflict."
He added: "We will not allow such inhumanity to deter us from continuing our partnership with the Government of Afghanistan. I have nothing but admiration for the staff of the Embassy, British and Afghan, who work at great personal risk to help build a better future for Afghanistan."
One British national and one Afghan working for the embassy were killed during an attack on a vehicle in Kabul this morning, Foreign Secretary Philip Hammond said.
Mr Hammond also condemned the attack on Twitter and said his thoughts are with the victims.
Condemn appalling attack on civilians supporting UK diplomatic activity in #Afghanistan. My thoughts are with the victims + their families
One British citizen has been killed in a suicide attack on a British embassy vehicle in Kabul, the Afghan Interior Ministry has said.
Four other people killed in the blast were Afghans. At least 33 people were also wounded.
At least five Afghan civilians were killed and up to 34 others hurt in a suicide attack on a British embassy vehicle, officials in the country said.
The attack caused parts of Kabul to shake and sent a plume of dust and smoke into the air.
Deputy interior minister General Mohammad Ayub Salangi said: "Foreign vehicles were targeted by a suicide attacker on a motorcycle."
The Taliban reportedly claimed responsibility for the attack.
The Afghan Taliban has claimed responsibility for an attack on a British embassy car in Kabul, Reuters news agency reports.
The blast reportedly killed five people and wounded several bystanders.
Five people have been killed in a suicide attack on a British embassy vehicle in the Afghan capital Kabul, including one embassy staff member, a local journalist has told ITV News.
Several others were also injured in the blast, the journalist said.
A suicide bomber who targeted a British embassy car was riding a motorcycle according to the Afghan deputy interior minister, General Ayoub Salangi.
The blast was powerful enough to wound 33 Afghan bystanders and destroy three cars nearby, Interior Ministry spokesman Sediq Sediqqi said.
A Foreign Office spokeswoman confirmed that a British Embassy vehicle was attacked in Kabul. She said: "A number of staff have been injured. We are working with the Afghan authorities to establish details of the incident."
A number of staff have been hurt in an attack on a British embassy vehicle in Afghanistan, the Foreign Office has said.