Lome - Two teenagers were among four people killed in violence in Togo's second city after an imam close to the main opposition was arrested, the government and a rights group said on Tuesday."Two soldiers on guard duty at the home of a VIP were lynched and executed and their weapons and ammunition were taken," the government said in a statement."A young person also died and about 20 other civilians and members of the security forces were injured," it added.Amnesty International's country representative Aime Adi told AFP the young person killed was an apprentice upholsterer and aged 16 or 17.A second youth, 17, was "shot in the head", he added.The clashes in the northern city of Sokode came against a backdrop of anti-government protests led by Tikpi Atchadam, from the Panafrican National Party (PNP).Atchadam has a power base in the city.Ouro Akpo Tchagnaou, from the National Alliance for Change (ANC) party, said: "Electricity was cut off at about 19:00 (2100 GMT on Monday) after evening prayers."Five police vehicles arrived to arrest Alpha Alassane, a very well-known imam in the city," he added. "The population felt targeted and took to the streets."Clashes lasted throughout the night until calm was restored but the authorities have been warned of renewed protests if Alassane is not freed on Tuesday morning."The situation was hard to put up with last night. The security forces and youths clashed in several parts of the city, with teargas and stone-throwing," one local told AFP."There were burning tyres, barricades erected and buildings were looted," added ANC spokesperson Eric Dupuy. "Homes were set on fire as well as a bank and premises belonging to (telephone company) TogoCell." Sporadic violence A local newspaper correspondent in Sokode told AFP the situation remained "very highly charged" on Tuesday afternoon."The young people have not left the barricades and the law enforcement is still firing teargas. The (main road between Togo and Burkina Faso) is still closed," he added.Togo's security minister Colonel Yark Damehame told the local Radio Victoire that the arrest of Alassane, who is close to the PNP, was justified."In his sermons he has been calling for violence and hatred... The last straw was last Friday when he called on his followers to kill soldiers," he said.The claims have been denied.In Bafilo, near Sokode, young people also took to the streets and erected barricades, blocking the main road, said a member of the opposition CAP 2015 coalition, Tchatchibara Akim.There were clashes in the Agoe area of Lome, which is a PNP stronghold. Two customs offices were set on fire and youths burned tyres, according to local residents.The suburb in the north of the capital was calm on Tuesday morning but there was a strong security presence.Opposition march Imam Alassane has long been a dissenting voice in Togo but his arrest comes at a time of heightened political tension in Togo in recent months.He has allied himself with the PNP of Atchadam, who has spearheaded protests against President Faure Gnassingbe that have mobilised hundreds of thousands across the country.The PNP and 13 other opposition parties are calling for political change in Togo to end the 50-year rule of the Gnassingbe family.They want a limit on the number of presidential mandates to two - in line with practice elsewhere in west Africa - and the introduction of a two-round voting system.The opposition parties have vowed to defy a government ban on midweek protests by marching in the capital Lome on Wednesday and on Thursday.