KANO, Nigeria (AP) - Radical Islamic fighters killed seven foreign hostages in Nigeria, European diplomats said Sunday, making it the worst such kidnapping violence in decades for a country beset by extremist guerrilla attacks. Nigeria's police, military, domestic spy service and presidency remained silent over the killings of the construction company workers, kidnapped Feb. 16 from northern Bauchi state. The government's silence only led to more questions about the nation's continued inability to halt attacks that have seen hundreds killed in shootings, church bombings and an attack on the United Nations. The latest victims were four Lebanese and one citizen apiece from Britain, Greece and Italy. Britain and Italy said all seven of those taken from the Setrapo construction company compound had died at the hands of Ansaru, a previously little-known splinter group of the Islamic sect Boko Haram. Greece also confirmed one of its citizens was killed, while Lebanese authorities didn't immediately comment. Italian Premier Mario Monti identified the slain Italian hostage as Silvano Trevisan and promised Rome would use "every effort" to stop the killers. British Foreign Secretary William Hague called the killings "an act of cold-blooded murder" and identified the U.K. victim as Brendan Vaughan. Ansaru issued a short statement Saturday saying its fighters kidnapped the foreigners from the construction company's camp at Jama'are, a town about 200 kilometers (125 miles) north of Bauchi, the capital of Bauchi state. In the attack, gunmen first assaulted a local prison and burned police trucks, authorities said. In an online statement Saturday claiming the killings, Ansaru said it killed the hostages in part because of local Nigerian journalists reporting on the arrival of British military aircraft to Bauchi. However, Ansaru's statement cited local news articles that instead said the airplanes were spotted at the international airport in Abuja, the nation's central capital about 180 miles (290 kilometers) southwest. The U.K. Defense Ministry said Sunday the planes it flew to Abuja ferried Nigerian troops and equipment to Bamako, Mali. The ministry declined to comment further. "I am grateful to the Nigerian government for their unstinting help and cooperation," Hague said in a statement, without addressing the claim that the U.K. had launched a rescue effort. Presidential spokesman Reuben Abati didn't respond to requests for comment Sunday. The majority of those attacks have been blamed on Boko Haram, an amorphous group that grew out of the remains of a sect that sparked a riot and a security crackdown in Nigeria in 2009 in which about 700 people killed. Boko Haram has hit international targets before, including an August 2011 car bombing of the U.N. office in Abuja that killed 25 people and wounded more than 100 others. The group is blamed for killing at least 792 people last year alone, according to an Associated Press count. Ansaru, which analysts believe split from Boko Haram in January 2012, seems to be focusing much more on Western targets. Analysts say it has closer links to al-Qaida in the Islamic Maghreb and cares more about international issues, as opposed to Boko Haram's largely local grievances. But much remains unknown about Ansaru, which so far has communicated through short, sometimes muddled online statements. The hostage killings appear to be the worst in decades targeting foreigners working in Nigeria, an oil-rich nation that's a major crude supplier to the U.S. Most kidnappings in the country's southern oil delta see foreigners released after companies pay ransoms. The latest kidnappings in Nigeria's predominantly Muslim north, however, have seen the hostages killed either by their captors or in military raids to free them, suggesting a new level of danger for expatriate workers there. The worst violence targeting foreign workers previously in the country's history came during its 1960s civil war. In May 1969, forces with the breakaway Republic of Biafra raided a Nigerian oil field, killing 10 Italian oil workers and a Jordanian. Eighteen other foreign workers taken by Biafran soldiers faced the death penalty, but later were pardoned and released. Associated Press writers Frances D'Emilio in Rome, Demetris Nellas in Athens, Greece, Sylvia Hui in London and Shehu Saulawa in Bauchi, Nigeria, contributed to this report.