Washington DC – President Joe Biden will attend Queen Elizabeth II’s funeral, officials have confirmed, amid reports that foreign heads of state will be escorted by bus and asked to not use their own cars or air transportation to travel in the UK.

Biden on the bus?

Dignitaries will travel to Westminster Abbey in escorted buses and "because of tight security and road restrictions" they will be required to leave their private state vehicles behind, according to leaked documents, seen by Politico.

It reported that only heads of state and their spouses or partners will be invited to the royal event on September 19, due to limited space within the historic building.

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It comes as the White House confirmed that Biden will attend the funeral, along with his wife Jill, after the monarch's death on Thursday.

Politico reported that a communication from the Foreign, Commonwealth and Development Office (FCDO) was sent to embassies late on Saturday.

The department said it "regrets that, because of limited space at the state funeral service and associated events, no other members of the principal guest’s family, staff or entourage may be admitted," it was reported.

Heads of state unable to attend may choose someone else as their official representative.

According to the document, world leaders have also been urged to travel on commercial flights and have been told they cannot use helicopters to travel around Britain.

The FCDO urged commercial travel "where possible," Politico said.

Security will also be extra tight.

"Multiple and comprehensive layers of security will be in place across London and at all the official venues used for the state funeral and associated events," according to a FCDO document seen by Politico.

Meanwhile, the use of helicopter transfers between airports and venues has been prohibited "due to the number of flights operating at this time," it was reported.

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Politico said that the document also set out some of the engagements for heads of state surrounding the funeral.

This includes receptions hosted by the king and the new Foreign Secretary James Cleverly, an offer to visit the queen’s body when it is lying in state, and to sign a book of condolence at Lancaster House.

It reported that foreign leaders will be invited to deliver a tribute to the queen while at Lancaster House, but it can only last up to three minutes.

And "because of the extensive ceremonial program to the state funeral and the logistical challenges, requests for bilaterals will not be considered on this occasion," according to the leaked document.

The FCDO has been approached for comment.