The 2009 cable from the US embassy in Mbabane recounts how the Swazi government blocked the parastatal Swaziland Post and Telecommunications Corporation (SPTC) from selling off its shares in multinational mobile firm MTN Group [JSE:MTN] to raise money for a new cell network project.
"Industry and press observers privately indicated to us that the king wanted to purchase the MTN shares himself at a cheaper price than the buyer... was offering SPTC," said the cable, which was released on Wednesday.
"The king had previously been able to buy strongly performing MTN shares at a low price, and he reportedly was annoyed he was not given that opportunity again."
The government also refused to renew the work permit of MTN Swaziland's chief executive, South African national Tebogo Mogapi, saying the decision was part of "localisation" efforts to bring more Swazis into high-level business positions.
But the cable said embassy contacts and press reports suggested the move was in fact "retaliation against the CEO for his role in the proposed share selling transaction to the highest bidder".
It said other observers reported that Mogapi was chased out because he "opposed government efforts to use the MTN network for electronic surveillance on political dissidents".
"Government officials would likely prefer a more malleable Swazi CEO at MTN who would cooperate more fully with royal and government wishes," it said.
Political parties have been banned in Swaziland, Africa's last absolute monarchy, since 1973.
Mswati - who has an estimated fortune of $100m (R720m) - has been facing mounting pressure for democratic reforms amid a financial crisis that has seen the tiny kingdom nearly run out of cash.
An IMF delegation is currently visiting Swaziland to gauge whether the kingdom has reformed its finances enough to win backing for international loans.