Yaound - Cameroon said on Wednesday its military offensive against Boko Haram across the Nigerian border has made major progress, with scores of jihadists killed and hundreds of hostages freed since December.But in a sign of continuing jihadist trouble, four would-be human bombs - two young boys and two teenaged girls - tried to strike in Cameroon's Far North province on Wednesday.Only the bombers died in the attempted attacks which were foiled by security forces and local vigilantes.Since Nigeria announced a key victory against Boko Haram jihadists in December, claiming the group had been routed from its Sambisa Forest bastion, its ally Cameroon has intensified operations along its northern border.Cameroonian troops have in recent weeks killed some 100 Boko Haram fighters and freed "hundreds of hostages" held by the group, Cameroon's government spokesperson Issa Tchiroma Bakary said on Tuesday.Some 30 other jihadists have been taken prisoner and returned to Nigeria. "Hundreds of freed hostages have [also] been sent back," Tchiroma said.With access to the combat zones tightly controlled, it was impossible to verify the government's claims.Cameroonian troops have been conducting cross-border operations alongside their Nigerian allies in the Nigerian village of Ngoshe since December 19, Tchiroma said."Unfortunately ... three [Cameroonian] soldiers lost their lives" in January, he said. One was killed in a blast, the other two in fighting.The operation, Tchiroma said, is being carried out "in perfect synergy with the [Nigerian] army command". He described it as a response to repeated incursions into Cameroonian territory by Boko Haram.On Wednesday, four young suicide bombers were killed in the restive Far North province, located just across the border from the epicentre of Boko Haram's insurgency in Nigeria, regional governor Midjiyawa Bakari said.Two vigilantes supporting the armed forces were lightly injured, he added.Cameroon's Far North province has been the frequent target of suicide attacks, with many of them carried out by children.Boko Haram's brutal insurgency, launched in northern Nigeria in 2009, has spread across the border to Cameroon, Chad and Niger. At least 20 000 people have been killed and some 2.6 million displaced in the violence.