Britain on Wednesday said deadly protests over Sudan's fuel price hikes should serve as a warning of the need for political dialogue, amid concerns for people detained in the crackdown.
Simon Fraser, permanent under-secretary in London's Foreign Office, said in Khartoum that he hoped "these protests will be a warning to everyone including the government that the situation needs to be addressed."
Authorities say 34 people died after petrol and diesel prices jumped on 23 September when the government cut fuel subsidies, sending thousands into the streets in the worst urban unrest during President Omar al-Bashir's 24-year rule.
Activists and international human rights groups said security forces shot dead at least 50 people, most of them in the greater Khartoum area.
At the end of a day-long visit to Khartoum, Fraser called for "an acceleration of a genuine process for comprehensive national dialogue."
"But that does require the commitment of all the parties, and in particular the government, to give confidence through its future actions," Fraser, who heads Britain's diplomatic service and is senior policy adviser to Foreign Secretary William Hague, told reporters.
Bashir called in April for dialogue with "all political powers" in his country, including armed rebels.
Along with insurgencies and an economic crisis, his ruling National Congress Party faces internal dissension.
Fraser met with government officials including Sudan's Foreign Minister Ali Karti, as well as civil society workers and others.
"We are also expressing our concern about the large number of detentions which have taken place and which I believe are still taking place, including a number of journalists and political activists," Fraser said.
Mark Lowcock, the top civil servant in Britain's Department for International Development, accompanied Fraser to Khartoum.
The husband of a social media activist who works for the World Bank told AFP that she is among those rounded up and has not been heard from since Monday.
Eight security officers took Dalia El Roubi from her family home, her husband Abdelrahman Elmahdi told AFP.
They also detained her friend Rayan Shaker, a fellow activist, but gave no reason for the arrests, Elmahdi said.
"As of today we have no clue as to her whereabouts or where she is staying or her condition," he said.
El Roubi had joined one protest last weekend, a funeral procession for Salah Sanhouri, a pharmacist gunned down during a demonstration, her husband said.
El Roubi is a communications specialist at the Khartoum office of the World Bank, a Washington-based institution which works to fight global poverty.
Sudan's government says it has arrested hundreds of "criminals" after the protests.
The government said it had to intervene last week when crowds turned violent, attacking petrol stations and police facilities.
The intensity of demonstrations has faded this week but witnesses on Wednesday reported three small rallies.
About 30 women stood silently in Khartoum near the military headquarters and Bashir's guest house, one witness said.
"We want justice for the martyrs and the injured," said a banner, while another sign called for freedom of expression, according to the witness.
A demonstration occurred at the University of Sudan's campus in South Khartoum but no details were immediately available.
In the Red Sea city of Port Sudan, up to 100 students took to the streets denouncing the regime, a witness said.
France, Britain and the United States have all expressed concern at Sudan's reaction to the protests.
In Khartoum, Fraser reiterated that Britain was "shocked and saddened" by reports Sudan's security forces had used excessive force.
He said he and Lowcock also "raised the question of media freedoms and the closure of some media outlets."
On Tuesday, the foreign ministry in Paris condemned the "disproportionate way" authorities responded to the demonstrations, and the "arbitrary arrests and media censorship."
Last week, Washington blasted the "brutal crackdown" and expressed alarm at reports that civil society activists had been detained, independent media outlets shut, and communications networks restricted.
The Committee to Protect Journalists, a New York-based watchdog, said late Tuesday that Sudan was using "censorship and intimidation" in an effort to make journalists stick to the official line about the protests.