Police in Sudan used tear gas Friday to break up the latest protests against austerity measures and the government of President Omar al-Bashir.

Witnesses say the rallies — of anywhere from a few dozen to a few hundred people — took place in the capital Khartoum and the suburbs of Omdurman and Bahri.

The tear gas was fired to disperse demonstrators who had gathered in the streets after Friday prayers.

Ahead of the rallies, the U.N. human rights chief called on Sudanese authorities not to use violence and mass arrests to stop the protests.

Navi Pillay, the U.N. high commissioner for human rights, said dozens of journalists, activists, and others have been arrested since the first student demonstrations began June 17.

The protests were sparked by President Bashir's announcement of sharp government spending cuts, including an end to a popular fuel subsidy. Many protesters have called for an end to the rule of Mr. Bashir and his National Congress Party.

An anti-government group known as GIRIFNA has listed a series of demands for Friday's protest, including the resignation of the government and the release of political prisoners.

The U.S. Embassy in Khartoum has warned American citizens in Sudan to exercise caution. It said in a statement Friday that U.S. citizens should avoid crowds or demonstrations, warning they could become confrontational or turn violent.

Earlier this week, the U.S. State Department condemned Sudan's response to the protests. Spokesperson Victoria Nuland said there have been reports of protesters being “beaten, imprisoned and severely mistreated while in government custody.”

President Bashir has dismissed the protests as the work of a few isolated agitators and vowed to continue with the planned spending cuts.

Sudan has seen revenue drop dramatically since neighboring South Sudan shut down oil production and stopped using northern pipelines.

South Sudan took control of about three-fourths of Sudan's oil output when it broke away and became independent last July.