Coca-Cola has been accused of propping up one of Africa's most notorious dictators.

The multibillion dollar beverage company owns a concentrate-manufacturing plant in Swaziland, an impoverished kingdom ruled by Africa's last absolute monarch, Mswati III.

The king has travelled to Coca-Cola's headquarters in Atlanta in the US, much to the disgust of Swazi political activists who blame him for human rights abuses and looting the nation's wealth.

Mary Pais Da Silva, co-ordinator of the Swaziland Democracy Campaign, called for Coca-Cola to pull out of the country immediately.

"Coca-Cola must know they're doing business with the wrong people," she said. "At the end of the day it doesn't benefit the economy in any way. Their profits don't help the average Swazi, while the king is getting richer by the day." She added: "The king is milking the country. This is entrenching him more and more, giving him economic strength to crush opposition. Nobody should do business with the regime in Swaziland. They should cut ties and take their business elsewhere."

Mswati III has 13 wives and hosts an annual dance where he can choose a new bride from tens of thousands of bare-breasted virgins.

With a fortune of about $100m (£64m), he presides over one of the worst-off countries in the world, with most people living in absolute poverty. Political parties are banned and activists are regularly arrested, imprisoned and tortured.

Coca-Cola says that Mswati III does not receive any profits or dividends from its Swaziland operation, its biggest in Africa. But some activists estimate that Coca-Cola, the world's biggest beverage company, contributes as much as 40% of the country's GDP. The company admits it cannot account for how the money it pays in taxes is used by the Swazi government.

Lucky Lukhele, a spokesman for Swaziland Solidarity Network, said: "Coca-Cola should find a way of directing the profits to the people of Swaziland. They should start supporting the pro-democracy movement."

He compared the moral imperative to that of boycotting South Africa during the racial apartheid years. "Many supported the people of South Africa. There is no such thing as neutral ground – you're for or against. The king is looting and destroying the economy. So either they support the people or they go into the dustbin of history along with the king."

He added: "It has become crazy in Swaziland. The people are desperate. They are dying from HIV/Aids and TB as the result of the misbehaviour of the king. There's enough evidence for the international criminal court to come in."

Coca-Cola says it adheres to the "highest ethical standards" and aims to be "an outstanding corporate citizen in every community we serve". It set up in Swaziland in 1987 after leaving apartheid South Africa.

It denies claims from some activists that it was motivated by Swaziland's sugarcane fields – its concentrates do not contain sugar – or that the king personally owns shares in the Swazi factory.

Sherree Shereni, spokeswoman for the Coca-Cola central Africa franchise, said: "King Mswati III does not receive any profits or dividends from Conco Swaziland [Coca-Cola's concentrate production plant]."

Conco, like all the Coca-Cola Company (TCCC) concentrate plants, is 100% owned by TCCC.

Shereni added: "Through the Coca-Cola Africa Foundation, which was set up in Swaziland in 2001, the population of Swaziland has, however, benefited from Coca-Cola's contributions to their social welfare in the areas of water stewardship, health, education and entrepreneurship."

Asked if the king uses tax revenue from Coca-Cola for his personal benefit, Shereni said: "TCCC, like any other taxpayer, does not determine what the taxes paid to the governments of countries in which it does business are used for. This is the statutory prerogative of the governments themselves."

She added: "Coca-Cola is not involved with political agenda of any country in which it does business. Coca-Cola's reputation is built on the quality of its brands, the highest standards of manufacturing practices, the welfare and safety of its employees and adherence to local and international laws as applicable in any country where Coca-Cola does business."