Foreign Secretary Jack Straw is flying to the US for talks amid violence in Uzbekistan in central Asia.
The foreign secretary has been quick to condemn the violence
Soldiers are reported to have killed unarmed civilians during a protest in the eastern town of Andijan on Friday.
Mr Straw has said this "plainly cannot be justified" and has demanded that aid agencies, diplomats and journalists be allowed access to the area.
He is also expected discuss the security situation in Iraq with US Secretary of State Condoleezza Rice.
And the pair are likely to consider Iran's nuclear programme during their meeting in Washington.
War on terror
Britain and the European Union have been quick to condemn the suppression of anti-government protests in the central Asian republic.
But the US views the country as a key ally in its war against terrorism, and has been slower to condemn the violence.
Local sources say several hundred people died when troops shot at unarmed protesters in Andijan.
The demo was sparked after a local businessman was arrested and put on trial for Islamic extremism.
Uzbek troops have sealed off Andijan and have so far refused access to journalists and the International Red Cross.