Three Malian civilians have been killed and around 30 people wounded in a suicide attack in the country's violence-hit north, officials said, as a diplomat said some of the injured were sub-contractors for the UN.The attack took place late on Monday in the city of Gao when a 4x4 vehicle blew up in a residential area, the security ministry said.The blast was claimed by the GSIM, the main jihadist group operating in the Sahel region. It has ties to al-Qaeda and was blacklisted by Washington in September. The GSIM - the Group to Support Islam and Muslims (GSIM) - said the attack had targeted "invading crusader forces" in central Gao in an area "where there are British, German and Canadian troops".A local official told AFP the fatalities were Malians who lived in the area. The government gave an initial toll of just two injured, but a French security source told AFP on Tuesday that the number of wounded had risen to "around 30". A Western diplomatic source also said four foreigners were among the wounded -- two Cambodians, a South African and a Zimbabwean.They were working for an organisation subcontracted by the UN's mine-clearing operation, UNMAS, which has a field office in the city, the source said.'Despicable' The attack was condemned by the French and German defence ministers as they visited Gao on Tuesday. "The attack last night in Gao was despicable. Once again, it is civilians who have paid for this violence with their lives," said French Defence Minister Florence Parly, echoing remarks by German counterpart Ursula von der Leyen.The French-German defence delegations had flown over to discuss Mali's troubled peace accord and plans to set up a five-nation anti-terror force in the vast, arid Sahel region. Mali has been struggling to return to stability after Islamist extremists took control of the north in early 2012, prompting a military intervention by France.The extremists were routed in the French operation in 2013 but large stretches of the landlocked African state remain out of government control.French praise for RAF Parly later visited the Gao military base where she thanked Britain's Royal Air Force personnel operating three heavy-lift Chinook helicopters in support of France's 4,500-strong Barkhane mission to the Sahel."Those who say France is alone in Mali are mistaken," she said, pointing to commitments from Estonia, Germany, Spain and the United States.The twin-rotor helicopters, operated by around 100 RAF personnel, can carry nearly four tonnes in supplies and more than 30 troops. Colonel Bertrand, who heads Barkhane's helicopter unit, said the Chinooks enabled the much faster resupply of forward positions 200km away as well as safety from the threat of roadside bombs. A British officer said that since the helicopters deployed in the summer they had been "very productive... We have been flying about 100 hours each month."