KHARTOUM - Sudanese police fired tear gas Tuesday at hundreds of teachers in Khartoum protesting the death of a colleague in detention as demonstrators pressed on with rallies against President Omar al-Bashir's rule.

Groups of doctors, students and lawyers also staged demonstrations in the capital and other areas of the country -- part of protests sparked by a government decision to triple the price of bread which have rocked Sudan since December 19.

The unrest quickly escalated into nationwide rallies against Bashir's three-decades in power, with demonstrators demanding the veteran leader step down.

Officials say 30 people have died in protest-related violence since then, but Human Rights Watch says at least 51 people have been killed.

Teachers on Tuesday rallied near the education ministry in Khartoum to protest the death of a fellow educator in the eastern state of Kassala, witnesses said, adding that riot police had fired tear gas to disperse the group.

Ahmed al-Kheir, a 36-year-old teacher and member of the Islamist Popular Congress Party (PCP), died in detention after security agents arrested him last week in connection to the protests.

Fellow teachers poured into the streets to chant for "freedom, peace, justice", a witness said, employing the rallying cry of the protest movement against Bashir's government.

"Many were carrying photographs of Kheir who died in detention," the witness added.

Kheir was a member of the PCP, which is part of Bashir's government but has called for a probe into the deaths of protesters killed during the rallies.

Police on Tuesday also fired tear gas at a separate demonstration launched by graduates of Khartoum University, witnesses said.

"The students were trying to stage a march, but they were dispersed with tear gas," a witness said.

Hundreds of doctors held sit-ins in several hospitals across the country calling on Bashir to step down, witnesses said.

Video footage uploaded onto social media showed doctors holding banners calling for Bashir's resignation.

About 200 lawyers held a separate march in Khartoum, but they were swiftly dispersed with tear gas, a lawyer said.

"We wanted to give a petition to the chief of the judiciary that calls for freedom of speech and the release of detainees," he said on condition of anonymity.

"But riot police fired tear gas at us, after which we had to disperse."