Two of Britain's biggest banks are under pressure for lending tens of millions of pounds to a technology company building a telecoms network that is part-owned and used by the Myanmar military, which is accused of committing genocide against the Rohingyas.

Human rights groups are demanding that the banks explain why they lent the money to such a company, The Observer, a sister concern of The Guardian, reported on Sunday.

HSBC and Standard Chartered have loaned $60m (£44.5m) to Vietnamese telecom giant Viettel in the last four years, a period when the Myanmar military has been accused of committing war crimes, genocide and crimes against humanity, said the report.

About 750,000 Rohingyas fled a brutal military campaign in Myanmar's Rakhine state and took shelter in Bangladesh in 2017. Myanmar now faces a genocide case at the International Court of Justice.

According to a report by the campaign group Justice For Myanmar (JFM), Viettel is a major investor in Mytel, a Myanmar mobile network that, since its launch in June 2018, has grown to become the second-biggest operator in the country with over 10 million users.

A Myanmar state-owned enterprise, Star High Co Ltd, a subsidiary of the military-operated Myanmar Economic Corporation, has a 28pc stake in the network; Viettel's international telecommunications investment subsidiary, Viettel Global JSC, controls 49pc; and Myanmar National Telecom Holdings, representing a group of Myanmar companies, owns 23pc.

The shareholding structure, which confirms Mytel is a major revenue generator for the Myanmar military, has been revealed by the JFM in a report, says The Observer.

JFM says Viettel units, under the Vietnamese Ministry of National Defence, are mining user-data for analysis in Vietnam. It alleges that the Myanmar military has access to the data, opening up the possibility it could be used for military purposes.

JFM has established that HSBC loaned $40m (£29.7m) to Viettel Global JSC between 2016 and 2020, while Standard Chartered's UK arm loaned just over $20m (£14.8m) over the same period.

"The report sets out very well the position of Mytel in relation to the Myanmar military and the position of Viettel in relation to Mytel," said Christopher Sidoti, a former member of the UN Human Rights Council's Independent International Fact-Finding Mission on Myanmar.

"The facts establish that Mytel plays a vital role for the military and that Viettel makes Mytel possible."

JFM says businesses with interests in Myanmar have responsibilities under UN human-rights principles and Organisation for Economic Co-operation and Development guidelines to uphold international standards on human rights. It also questions whether HSBC and Standard Chartered may be in breach of EU restrictive measures on Myanmar.

"The report reflects where the money trail leads," Sidoti said. "Among other places, it leads to HSBC and Standard Chartered. The report does this very cautiously, conservatively, not asserting that HSBC and Standard Chartered are liable for prosecution for crimes under international law or that they are directly aiding and abetting the commission of such crimes. Rather, the report puts these companies into a third category of entities that have human-rights due-diligence responsibilities that they have breached. That is a conclusion with which I agree."

Yadanar Maung, a spokesman for JFM, said: "HSBC and Standard Chartered should be transparent and show exactly how they monitor and prevent their loans from financing human rights abuses."

HSBC told The Observer: "HSBC complies with sanctions, laws and regulations in all the jurisdictions in which we operate and strongly supports observance of international human rights principles as they apply to business. We do not comment on client relationships, even to confirm or deny that a relationship exists."

Standard Chartered declined to comment.