Khartoum - Hundreds of protesters, mostly students, took to the streets in and near Sudan's capital Khartoum on Monday, continuing a three-month wave of demonstrations that has posed the most serious challenge yet to President Omar al-Bashir's three-decade rule.

Students, activists and other protesters frustrated with economic hardships have held almost daily demonstrations across Sudan since Dec. 19, calling for Bashir to step down.

Police used tear gas on Monday to disperse hundreds of students from Eastern Nile University protesting in Khartoum North, and hundreds of other demonstrators on Sitteen Street, which runs through several upscale neighbourhoods, witnesses said.

At least four demonstrators were detained on Monday by security forces in Khartoum 2, an upscale area in the heart of the capital where dozens protested, a Reuters witness said.

Security forces used batons to disperse the demonstrators, some of whom torched car tyres.

Police have used tear gas, batons and sometimes live ammunition to break up protests. Officials have confirmed 33 deaths in the unrest since December, but activists say the toll is significantly higher.

Opposition organisers often give the protests a theme for the day - Monday's were for "student martyrs". Demonstrations on Sunday, which drew thousands in and near Khartoum, were for "graduates and the unemployed".

Bashir, who took power in a military coup in 1989, promised during a swearing-in ceremony for a new cabinet last week that he would engage in dialogue with the opposition. The opposition has rejected dialogue with Bashir and has continued to call for him and his government to step aside.

Last month Bashir declared a state of emergency, dissolved the central government, replaced state governors with security officials, expanded police powers and banned unlicensed public gatherings.

That has not stopped the protesters, who have stepped up demonstrations in recent days.

Sudan secures $300M loans

Sudan says it has signed agreements for $300 million in loans from a regional monetary fund to help address a foreign currency crisis that has fueled months of anti-government protests.

The state-run SUNA news service reported late Saturday that the Finance Ministry secured a $230 million loan from the Arab Monetary Fund to support the balance of payments.

It says the ministry signed another deal worth $70 million with the Arab Trade Financing Program.

The demonstrations began in December over price hikes and food shortages, and quickly escalated into calls for President Omar al-Bashir to step down, posing one of the biggest challenges yet to his nearly 30-year rule.

The rallies are being led by the Sudanese Professionals Association, an umbrella group of independent professional unions. Footage posted online showed dozens of people marching in Khartoum and its twin city of Omdurman, chanting: "Freedom, dignity and justice."

Al Bashir, who seized power in an Islamist-backed military coup in 1989, has responded to the protests by suspending plans for constitutional amendments that would allow him to seek a new term in next year's elections. He has also stepped down as leader of the ruling party, appointing a loyalist in his place.

Critics say he is trying to buy time and remain in power.