The cable released by the whistleblowing WikiLeaks site detailed a conversation between International Criminal Court Chief Prosecutor Luis Moreno-Ocampo and a top US diplomat in March 2009.
The cable was sent shortly after the ICC issued an arrest warrant for al-Bashir for alleged war crimes carried out during years of conflict in Sudan's restive Darfur province. Moreno-Ocampo told Alejandro D Wolff, the former US ambassador to the UN, that revealing al-Bashir had stolen public funds could aid efforts to arrest the Sudanese leader - who is still running his country despite three counts of genocide being added to the warrant in July.
"Ocampo suggested if Bashir's stash of money were disclosed (he put the figure at possibly $9 billion), it would change Sudanese public opinion from him being a 'crusader' to that of a thief," the cable said.
While Sudan is rich in oil, many of its residents live in poverty.
According to the cable Moreno-Ocampo reported: "Lloyd's Bank in London might be holding or knowledgeable of the whereabouts of his money."
Lloyds Banking Group quickly moved to answer the charges.
"We have absolutely no evidence to suggest there is any connection between Lloyds Banking Group and Bashir," the bank said. "The group's policy is to abide by the legal and regulatory obligations in all jurisdictions in which we operate."
Sudan also denied there was any truth to the accusation.
"To claim that the president can control the treasury and take money to put into his own accounts is ludicrous - it is a laughable claim by the ICC prosecutor," Khalid al-Mubarak, a spokesman at Sudan's London embassy, told the Guardian.
The accusations come as Sudan prepares for a Jan 9 referendum that is widely expected to see Southern Sudan vote to separate from the north and has raised fears of a return to conflict.
Sudan's mainly Muslim north and Christian and Animist south fought a decades-long civil war, during which an estimated two million died and four million were displaced. The conflict was prompted in part by accusations of inequitable distributions of wealth, and southern leaders have accused al-Bashir's government of cheating them out of revenues due from Sudan's oil since a peace deal was signed in 2005.
Global Witness, a watchdog that tracks resource-based conflict, said the accusations that al-Bashir has been creaming off money could raise tensions already high ahead of the referendum.
"If the cable is true, more than just doing business with an indicted war criminal, Lloyd's could be in some sense contributing to instability and mistrust in Sudan at the most fragile moment in its history," Global Witness campaigner Robert Palmer said.