Thousands are demonstrating Friday in a string of neighbourhoods of the Sudanese capital of Khartoum, calling for President Omar al-Bashir to step down, according to activists, keeping up the pressure on the autocratic general-turned-president who has been in power for nearly 30 years.The activists said hundreds also took to the streets on Friday in the railway city of Atbara north of Khartoum, Obeid in the western North Kordofan province, and Senar and Wad Madani south of the capital. They spoke on condition of anonymity because they feared reprisals.Friday's protests were the latest in a wave of demonstrations that began across much of Sudan on December 19, first against price rises and shortages but which later turned against Bashir, in power since a 1989 military coup he led. They coincide with worsening economic woes that saw a currency devaluation spiking prices, fuel shortages and a steep rise in the price of bread, a main fare to most Sudanese.As in previous protests, participants were numbered in the hundreds or the very low thousands, but the continuing defiance of the government in the face of security forces that have reportedly killed scores and injured hundreds speak of a high level of popular discontent.It's too soon to speculate on whether these relatively modest numbers could force Bashir to step down, but they might embolden top army commanders to counsel the president to quit in the nation's interest, although another general at the helm is unlikely to placate the Sudanese. A protracted uprising would paralyze the country and turn into the kind of chaos seen in Libya, whose 2011 revolt turned into a civil war that has left the country divided to this day.Sudan's military has dominated the country since independence in 1956 and the ongoing protest bear some resemblance to popular revolts in 1964 and 1985 that toppled military regimes.The protesters in Atbara chanted "the people want to bring down the regime," the main slogan of the Arab Spring revolts of 2010 and 2011. In the Khartoum suburb of Omdurman, they chanted "freedom, peace and justice."A video clip provided by the activists and posted online purported to show the scene at a Khartoum mosque where Bashir, an Islamist, performed the Friday prayers. A lone male voice could be heard shouting "Bashir, leave!"Friday's protests also coincided with an indefinite strike by doctors and a three-day strike by journalists that began on Thursday.Also on Friday, the activists reported another wave of arrests of opposition leaders, including some of the organisers of an attempted march on Bashir's presidential palace on Tuesday. The call for the march attracted thousands of participants who clashed with police who used tear gas and rubber bullets to disperse them. Scores were wounded, some seriously.London-based rights group Amnesty International says it has "reliable reports" to show that 37 people were killed in the first five days of unrest. The United States, Britain, Canada and Norway have expressed concern about the use of lethal force by security forces against protesters and are demanding an investigation.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.