Barclays was Thursday night close to securing a capital injection worth around £6bn from Middle Eastern governments, including Qatar and Abu Dhabi, in a move that will allow the UK bank to boost its balance sheet without turning to the British state for cash.

Barclays executives were last night finalising the terms of the capital increase with investors including the Qatar Investment Authority and an Abu Dhabi-based sovereign wealth fund.

An announcement could be made as early as Friday, although people involved in the negotiations warned they could still fall apart or drag into the weekend.

Barclays also held detailed discussions with Libya’s sovereign wealth fund about participating in the fundraising. Late last night, however, the likelihood of the Libyan Investment Authority participating in the deal appeared to have receded.

If completed, the cash injection will largely fulfil Barclays’ pledge to raise £6.5bn in fresh capital as part of the state-sponsored recapitalisation of Britain’s largest banks.

It will also surprise rival bankers and government officials who have been deeply sceptical about Barclays’ ability to raise so much capital without government support.

Barclays surprised rivals and regulators this month when it chose not to participate in the recapitalisation that saw the government inject up to £37bn into Royal Bank of Scotland, HBOS and Lloyds TSB. Although regulators forced Barclays to boost its capital reserves by more than £10bn by issuing equity, selling assets and slashing its final dividend for 2008, the bank insisted it would raise the money privately.

Barclays is expected to issue a range of complex capital instruments to its new investors. It is also expected to give existing shareholders the opportunity to participate in the fundraising.

Barclays’ search for capital has been led by Roger Jenkins, a long-serving executive who is chairman of its investment banking and investment management operations in the Middle East. In recent months, Mr Jenkins and his team have contacted a large number of investors to gauge their interest in investing in Barclays.

If completed, Barclays’ capital increase will mark the second time in six months that the bank has turned to the Middle East for fresh capital. The QIA already has a large stake in Barclays after participating in the bank’s £4.5bn capital increase – priced at 282p a share – earlier this year. Last night Barclays shares closed at 205.25p, up 14.95p.

Under a plan agreed with the Financial Services Authority, Barclays has been given until the end of the year to raise £3bn in preference shares, and until March to raise a further £3.5bn in ordinary shares. If the bank fails to secure private capital it will be forced to turn to the UK government, which is likely to impose onerous terms on any capital injection, and could demand the resignations of senior executives including John Varley, Barclays’ chief executive.

Additional reporting by Roula Khalaf