At least three Afghan policemen have been killed in a roadside bombing near the Pakistan border, officials say.
The police vehicle was badly damaged
Two other officers were hurt in the blast near the eastern city of Khost.
Hours earlier, three British soldiers and an Afghan were hurt in what Afghan officials said was a suicide car bomb attack in southern Helmand province.
Attacks blamed on al-Qaeda and Taleban militants, particularly in southern and eastern Afghanistan, have soared in recent months.
The remote-controlled device which killed the policemen was intended to target US troops, the governor of Daomanda district, Sayed Ahmed Khan Waffa, told the BBC.
He blamed the Taleban and al-Qaeda for the attack, which came on the main Khost-Kabul road about 40km (25 miles) west of Khost.
Governor Waffa said a US patrol had passed the blast site shortly before.
The force of the blast blew a crater in the road and threw the police vehicle at least 15 metres away, the BBC's Bilal Sarwary reported from the scene.
The attack on UK troops happened near the entrance to a military base in the provincial capital, Lashkar Gah.
It was the latest in a series of suicide attacks or attempts reported on Nato forces since the beginning of the year.
A spokesman for British forces in southern Afghanistan said: "There was an attack with a vehicle-borne improvised explosive device."
One soldier was treated at the scene and two others taken to a military hospital, he added.
Several thousand British soldiers are deploying in Helmand over the coming months as part of a big expansion of Nato's operations in Afghanistan.
The province is Afghanistan's biggest poppy growing area.