Several international human rights groups are calling for the government of South Sudan to release two journalists detained after the publication of an article criticizing South Sudanese President Salva Kiir.

Peter Ngor Arol Garang and Dengdit Ayok were arrested earlier this month and are believed to be held without charge by Sudan's National Security Services.

The arrests came after Garang, an editor at The Destiny newspaper in the capital of Juba, published an article by Ayok criticizing President Kiir for “staining his patriotism” by allowing his daughter to marry an Ethiopian man.

On Tuesday, Amnesty International called for the immediate release of both men, saying their detentions were an “outrageous attack on freedom of expression.”

Reporters Without Borders also condemned the arrests and urged South Sudan to pass laws protecting journalists from arbitrary imprisonment.

Sudan Tribune, where Garang is also employed, issued a statement Wednesday urging the United Nations to pressure South Sudanese authorities to free both journalists.

The paper said it “does not support the sentiments of the article,” but that it supports the men's right to freedom of expression.

Sudanese authorities suspended indefinitely publication of The Destiny on November 1. Before it was shut down, the paper published a public apology to President Kiir.

The Committee to Protect Journalists said this week it was “alarming to see the world's newest nation already arresting journalists.”

Rights groups have voiced repeated concerns about South Sudan's treatment of journalists following its independence from Sudan in July.