On Lockerbie, the Senate Foreign Relations Committee wants the UK to conduct an investigation.

WHITEHOUSE: Press Briefing

It commemorates the day in 1919 when the UK gave up control of Afghanistan's foreign relations following a short border war.

BBC: Taleban 'ambush Afghan police'

Mr Menendez, along with three other senators, launched the investigation after officials from Scotland, the UK and BP did not testify at a Senate foreign relations committee hearing, he was scheduled to chair in July.

BBC: US Lockerbie report: Scotland pressured to free Megrahi

Meanwhile, Iranian Foreign minister Manouchehr Mottaki confirmed Tehran was looking at relations with the UK following the tit-for-tat diplomatic expulsions.

CNN: Report: Iran to 'review' UK relations as tensions mount

Mr Straw, the first UK foreign secretary to visit Tehran since the 1979 Islamic revolution, will also discuss bilateral relations.

BBC: UK rallies Iran's support