Julian Assange’s belongings from his time living in the Ecuadorian embassy in London will be handed over to US prosecutors on Monday, according to WikiLeaks.

Ecuadorian officials are travelling to London to allow US prosecutors to “help themselves” to items including legal papers, medical records and electronic equipment, it was claimed.

WikiLeaks said UN officials and Assange’s lawyers were being stopped from being present. Lawyers said it was an illegal seizure of property, which has been requested by the US authorities. The material is said to include two of Assange’s manuscripts.

Assange was dragged out of the embassy last month and is serving a 50-week prison sentence for bail violations. He faces an extradition request from the US next month.

Kristinn Hrafnsson, the editor-in-chief of WikiLeaks, said: “On Monday, Ecuador will perform a puppet show at the embassy of Ecuador in London for their masters in Washington, just in time to expand their extradition case before the UK deadline on 14 June. The Trump administration is inducing its allies to behave like it’s the wild west.”

Baltasar Garzón, the international legal coordinator for the defence of Assange and WikiLeaks, said: “It is extremely worrying that Ecuador has proceeded with the search and seizure of property, documents, information and other material belonging to the defence of Julian Assange, which Ecuador arbitrarily confiscated, so that these can be handed over to the the agent of political persecution against him, the United States.

“It is an unprecedented attack on the rights of the defence, freedom of expression and access to information exposing massive human rights abuses and corruption. We call on international protection institutions to intervene to put a stop to this persecution.”