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A US senator has asked the Scottish government to reconsider its decision not to send officials to a hearing into the release of the Lockerbie bomber.

In a letter, Frank Lautenberg said he was "pleading" with First Minister Alex Salmond to help shed light on claims that BP had influenced the release.

Mr Salmond has declined an invitation to send his justice secretary and a medical expert to Washington.

The UK Foreign Secretary said the release was "wrong and misguided".

William Hague wrote to US senators on Saturday, after former UK Justice Secretary Jack Straw also chose not to attend the Washington hearings.

Abdelbaset Ali al-Megrahi, who was convicted of blowing up a Pan Am jumbo jet over the town of Lockerbie in 1988 in which 270 people were killed, was freed by the Scottish government on medical grounds last August.

In his letter to Mr Salmond, the New Jersey senator expresses frustration at what he portrays as the UK and Scottish governments blaming each other for this row.

He says the grief of victims' families has been "amplified" by allegations of improprieties surrounding the release.

Mr Lautenberg said: "I am pleading for direct representation from the Scottish government at our hearing next week to help us seek answers.

"Your co-operation in sending a knowledgeable person will help establish a credible record of what transpired."

US politicians are concerned that the decision to free Megrahi may have been tied to an oil deal involving BP.

On Friday, Scottish Justice Secretary Kenny MacAskill defended his decision not to attend the US hearing.

He said he was "accountable to Scotland" and had "no information to provide" on any BP oil deal.

In his letter to the senators Mr Hague criticised the release of Megrahi, but said it was "legally and constitutionally proper" that the decision was one for the Scottish government.

Mr Hague has previously acknowledged that BP did lobby the previous Labour government in favour of a prisoner transfer agreement between Britain and Libya.

But Mr Hague pointed out that Megrahi was freed by the Scottish government on entirely separate, compassionate grounds because the prisoner was deemed to be terminally ill.

Prime Minister David Cameron met Mr Lautenberg and three other senators from New York and New Jersey, where many of the Lockerbie bombing victims came from, during his visit to Washington this week.

He said he had seen no evidence that the Scottish government - which made the decision to free terminally ill cancer patient Megrahi on compassionate grounds - had been "swayed" by lobbying from BP.