The employer of the two South African air crew being held in Equatorial Guinea will consult Amnesty International if talks between the two governments do not secure their release.
Global Aircraft Leasing (GAL) chief executive Daniel Rosenzweig said on Thursday: "To be fair on the department of foreign affairs, if their talks are still not going anywhere, we must go the next step and take it up with Amnesty."
His staffers, Sechan Pillay and Ruwayda Kalbine, have been held against their will in Equatorial Guinea for two weeks while two companies involved in a string of aviation sub-contracts bicker about payments.
Rosenzweig said: "I am frustrated; they (foreign affairs) do not seem to be taking this with any degree of urgency.
"I would dearly like foreign affairs to be more proactive and urgent in what they are doing, but there does not seem to be a sense of urgency about what they are doing."
'Don't bother about diplomacy'
He said Equatorial Guinea was known for the lack of rule of law.
"They do not bother about diplomatic connections with South Africa or anyone."
Foreign affairs spokesperson Nomfanelo Kota would not comment on Rosenzweig's remarks.
One of the companies involved, local airline Guinea Ecuatorial de Transportes Aereos (Getra) is partly owned by the west African country's finance minister Mereelino Owono Edu, said Rosenzweig.
"It is alleged that the minister of finance had denied them permission to leave the country."
Rosenzweig said sending any more GAL staff to Equatorial Guinea to fetch the two would be risky, as they, too, might be taken hostage.
"We can consider (going to Equatorial Guinea to negotiate), but not while people are being held hostage. It's not a quid pro quo. We want our people out."
That six South African mercenaries were in jail for plotting a coup in Equatorial Guinea could be contributing to the impasse, he said.