Bank of America will stop supplying U.S. dollars to Angola at the end of this month, two foreign exchange sources said on Thursday, a move that could pile pressure on the oil exporter's ailing kwanza.

South Africa's Rand Merchant Bank said on Thursday that a U.S. bank had decided to discontinue providing it with dollars for onward supply to Angola which meant it would stop selling Angolan banks the greenback from Nov. 30.

RMB, a division of FirstRand Bank Ltd., did not name the U.S. bank or say why it no longer wished to trade dollars with Angola. Bank of America, the biggest supplier of dollars to Angola, declined to comment.

Angola's kwanza has weakened around 30 percent officially this year and far more on the parallel market as subdued oil prices hit Africa's second largest crude exporter.

Angola's central bank said on Nov. 5 that it would reduce the delivery of banknotes in foreign currency to travelers as well as limit withdrawals from foreign currency accounts as it sought to stem the kwanza's slide.

In September, Angola's central bank devalued the kwanza by about 4 percent and tightened dollar liquidity after a devaluation of 6 percent in June. But the currency has continued to weaken and analysts are expecting a further devaluation soon.

Former Portuguese colony Angola is an increasingly important market for global powers. The southern African country is a key oil supplier to China and sold its first Eurobond this month, raising $1.5 billion via a 10-year issue.