Thirteen separatists in an oil-rich enclave on Africa's west coast ruled by Angola have been acquitted of charges of crimes against state security, local media said on Friday.The activists are members of a small secessionist group, the Cabinda Independence Movement, whose organisation is seeking "dialogue" with Luanda on holding a referendum on self-determination.They were arrested last Friday during a meeting to organise a public debate on the enclave's autonomy.They were charged with crime against state security. The interior ministry said "hostile propaganda material” had been seized.In court, the activists said they had informed the authorities of the planned debate and even invited Cabinda's provincial governor, political parties and churches to participate in it.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook. The judge ruled that the meeting was not illegal."Angolan police should stop treating activists as enemies of the state," Zenaida Machado, Angola specialist at Human Rights Watch, told AFP."Peaceful meetings to arbitrarily arrest people is not only a shameful abuse, it is also an embarrassment for the Angolan government," she said.Machado said the decision to drop the charges was "encouraging.""We hope this trend is here to stay," said Machado.A lawyer for the activists, Arao Bula Tempo, also hailed "the independence of the court".Cabinda is a coastal exclave with the status of a province of Angola. It produces 60% of Angola's oil.It shares a northern border with the Republic of Congo, and a southern border with the Democratic Republic of Congo, which has a narrow strip of territory giving it access to the sea.Cabinda has been rocked by a separatist insurgency since it officially became part of Angola at independence.The Front for the Liberation of the Enclave of Cabinda (FLEC), is by far the largest separatist movement. It has been fighting for the independence for four decades.