Security forces tightened their grip on restive northern Nigeria Tuesday as they hunted for the perpetrators of a spate of bombings that has left at least 30 people dead in just two days, including two girls. In the latest attack, two girls were killed and three customs officers wounded in the northeastern city of Maiduguri on Monday, according to army officials, although residents and witnesses put the death toll at about a dozen. A day earlier, suspected Islamist extremists tossed bombs and fired on a crowded beer garden in the same city, killing 25 people. There was no claim of responsibility for the twin attacks. But suspicion fell on the shadowy sect Boko Haram, which is blamed for almost daily attacks targeting police, military personnel and politicians as well as community and religious leaders in parts of northeastern Borno state, especially Maiduguri. Tuesday, army troops frisked passers-by and vehicles amid tightened security in the wake of the bombings. \"Army checkpoints are all over the city. The military conduct searches on vehicles and passengers while patrol teams comb the streets,\" said local resident Haruna Mohammad. General Ralph Isah, commander of the Joint Task Force (JTF) in Maiduguri, said army, navy, air force, police, customs, immigration and intelligence personnel were involved in the operation and would remain deployed until calm was restored. Boko Haram, whose name means \"Western education is a sin\", launched an uprising in 2009 which was brutally put down by the military in an assault that left more than 800 people dead, mainly sect members, including its leader Mohammed Yusuf. The sect wants establishment of an Islamic state in the north and the strict application of Sharia law. European Union and United States diplomats in Nigeria on Tuesday jointly condemned Sunday\'s gun and bomb attacks, describing them in a statement as \"an affront to the rule of law and democratic principles\". \"There is no place in society for these horrific acts of violence and there should be no impunity for the perpetrators,\" the statement added. Amnesty International slammed the latest attack and urged Nigerian armed groups to stop their \"senseless\" killings of civilians.It specifically called on Boko Haram to end its \"reign of terror.\" \"These killings are senseless and outrageous. Direct attacks on civilians are prohibited under international law and show a complete disregard for the right to life,\" Tawanda Hondora, Amnesty\'s deputy director for Africa, said in a statement. Boko Haram has said that some of its members received training in Somalia, indicating some ties with Al-Qaeda-linked groups such as Al Shebab. Some of the sect\'s members are also believed to have been trained in Algeria and Afghanistan. Initially made up of university graduates and dropouts from wealthy and middle-class families, Boko Haram, which initially went by the name the \"Nigerian Taliban\", made its debut in January 2004. The festering violence is a major challenge for President Goodluck Jonathan, who has had to contend with bombings since he was sworn into office on May 29 following his election for a first full term in April. This country of 150 million people, almost evenly distributed between Christians and Muslims, is also wracked by ethnic and religious violence violence in Jos, the fractured capital of Nigeria\'s central Plateau state. Jos, a city of roughly under a million people that acts as a buffer between the predominantly Muslim north and the mainly Christian south, is split into two main factions -- Muslim and Christian.