Kinshasa (AFP) - Opposition campaigners launched a two-day general strike Tuesday to pressure Congolese President Joseph Kabila to set an election date -- a day after 12 people were shot dead during an anti-government rampage in the capital.

More than 40 people have been detained over the clashes in Kinshasa, an AFP reporter said.

The "dead city" action, organised well before Monday's killings, was to turn up the heat on Kabila, who is still in power despite his mandate expiring last year.

While Kinshasa did not grind to a total halt, two-thirds of shops and banks were closed, AFP journalists reported, while soldiers and police were out in strength.

The government also wrote to mobile phone operators calling on them to limit the "abusive" use of social media, in what appeared to be a bid to stop photos being posted of the protests which were also taking place in other cities.

"The city is paralysed," Kinshasa resident Kiki Kalombo told AFP.

"It's to make Corneille Nangaa put out a calendar for the elections," he added, referring to the electoral commission chief.

Nangaa has already said his organisation cannot organise a presidential poll as anticipated by year's end.

"Traffic is quiet, but we are still at work," government spokesman Lambert Mende told AFP.

In the southeastern regional capital of Lubumbashi, the main fish market was closed after youths clashed with security forces. Elsewhere in the city, however, it was business as usual.

And in Goma, the capital of North Kivu province in the restive east, riot police were posted at all main city junctions, an AFP correspondent said. A few dozen youths using rocks tried to barricade some streets.

- Anti-Kabila rampage -

Police say Monday's killings came as the anti-Kabila Bundu Dia Mayala group went on a rampage, attacking security forces in several Kinshasa neighbourhoods.

Members of the group, sporting red bandanas, sprung their attack while chanting "prayers and slogans hostile to legally established institutions," said police spokesman Pierrot Rombaut Mwanamputu on Monday.

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The victims were hit by stray bullets, he added.

An AFP reporter saw at least 46 suspected Bundu Dia Mayala members being held at Kinshasa's national police headquarters.

While many Kinshasa residents backed Tuesday's strike against Kabila, not everyone was happy.

"The 'dead city' policy has never come up with the hoped-for results," said Alexander, owner of a fish store.

"My business is shut. I've lost clients. The economy is on its knees," he said.

In his eyes, a strongman was needed to force out Kabila, who came to power in 2001 after the assassination of his father Laurent.

The political instability in the vast country of 70 million has raised international concerns, and a top UN official in Kinshasa Monday met with the government to discuss ways to expedite elections.

- Kasai bloodshed -

Ahead of this week's protests, Prime Minister Bruno Tshibala insisted DR Congo was "on course" for elections.

But he failed to give the opposition the detailed timeline they have been demanding for months.

One of the main obstacles to organising polls is the continuing violence in the central, diamond-rich Kasai region where a rebellion has been going on for a year now, according to the electoral commission chief.

Both the government and rebels are accused of atrocities in Kasai.

Last week a UN report detailed more than 250 "extrajudicial or targeted killings" of Kasai civilians earlier this year, with dozens of children among the victims.

Detailing cases of people being burned alive or mutilated, the report blamed government troops as well as militia groups on both sides of the conflict.