Scottish government officials have again turned down a plea to send a representative to a US congressional hearing into the release of the Lockerbie bomber.
Abdel Basset al-Megrahi, the only person convicted over the 1988 bombing, was released from prison by Scotland last year on compassionate grounds, because he has terminal cancer.
United States senator Frank Lautenberg has written to the first minister of Scotland, Alex Salmond, "pleading" for direct representation from the Scottish government at the hearing this week.
Two Scottish officials have already declined to appear before the Senate Foreign Relations Committee, which is examining the circumstances of the release.
Scottish justice secretary Kenny MacAskill has again refused to attend.
The committee hearing scheduled for 29 July also is looking into whether BP's oil interests influenced the bomber's release.
BP has denied it pushed Scottish authorities to release the bomber in 2009, and Scottish authorities have also denied there was any such contact with BP.
The bombing of Pan Am flight 103 killed 270 people, most of them Americans.
