Sudanese security agents confiscated entire print-runs of three newspapers this week in what media watchdog Reporters Without Borders (RSF) said on Thursday was a new drive to "gag" press freedom in the African nation.

Agents of Sudan's powerful National Intelligence and Security Service (NISS) confiscated copies of Al-Tayar, Alyoum Altaly and Al-Jareeda over the past few days and also interrogated some journalists for covering "sensitive issues", the media watchdog said in a statement.

RSF said the entire print-runs of Al-Tayar were seized on 10 and 11 June in the latest bid by NISS agents to "gag the press" after it published a column that said President Omar al-Bashir's resignation might help in reviving the country's ailing economy.

"They reminded me that there are red lines and that I should have known the president was one of them," Al-Tayar reporter Shamael al-Nur, who wrote the column on 9 June, was quoted as saying by RSF after she was twice interrogated by NISS agents.

Security agents seized copies of Alyoum Altaly on Wednesday, just days after preventing Al-Jareeda from distributing its copies in Khartoum, RSF said.

"The NISS must stop operating as an editorial police that censors journalists and systematically suppresses any critical publication, listing taboo subjects as it pleases," head of RSF's Africa desk, Arnaud Froger, said in the statement.

"The survival of a free press in Sudan is at stake."

Security agents seized copies of several newspapers in a similar crackdown in January after they criticised the government over soaring bread prices.

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Media in Sudan are frequently targeted by NISS agents for their reporting, especially for publishing articles against government policies.

RSF ranked Sudan 174th out of 180 countries on its 2017 World Press Freedom Index, saying that NISS "hounds journalists and censors the print media".

In an annual report on Sudan, Human Rights Watch earlier denounced Khartoum's suppression of freedom of expression.

"Security officials continued to restrict media by harassing and detaining journalists, charging them with crimes, and confiscating editions of newspapers that published articles deemed too sensitive," the rights group said.