MADRID , Spain ( CNN ) -- A car bomb exploded Thursday in a parking lot at the University of Navarra in Pamplona , Spain , sparking a massive fire , but `` luckily , '' no one was nearby and there were no deaths , Spain 's interior minister said . `` There could have been an enormous tragedy today at the University of Navarra , '' Interior Minister Alfredo Perez Rubalcaba said hours after the attack in a televised address . Hospital officials told CNN that 27 people suffered minor injuries , including one American woman and five other non-Spaniards . The Basque separatist group ETA is suspected to be behind the attack . The car , packed with an unknown quantity of explosives , was parked in a lot near the university 's library and detonated shortly after 11 a.m. local time ( 6 a.m . ET ) , Rubalcaba said . Watch witness describe the blast » . Campus authorities shut down the entire campus shortly after the blast to search for a possible second explosive device near the science building , about a half kilometer ( .3 mile ) from the car bombing , according to CNN 's partner station in Spain , CNN+ . Watch report on Pamplona car bomb » . No device was found and the search was called off Thursday afternoon , according to a university spokesman and a representative for the national government 's main office in Navarra . Most of the campus was reopened ; only the area surrounding the bomb blast remained cordoned off , they said . Classes are expected to resume as scheduled on Friday , the university spokesman said . The car bomb sparked a massive fire in the campus ' Central Building , where about 400 students and staff were located at the time , university spokesman Jesus Diaz told CNN+ . Video from the scene showed fire engulfing part of the building and thick clouds of black smoke billowing over the campus . Authorities in Spain 's Basque province of Alava received a warning call at 9:50 a.m. in the name of ETA . Watch aftermath of the blast » . The warning call to the DYA emergency services in Alava said the car bomb would strike a university campus in the city of Vitoria about an hour after the phone call , prompting emergency officials to search that campus and determine that the call was merely a false alarm , Rubalcaba said . `` So whoever planted the bomb either gave an intentionally misleading warning call or they made a mistake , '' he said in his televised address . According to CNN+ , the University of Navarra has been targeted by ETA six times in the past 30 years , and one faculty member said it is unclear why . `` It is not a political university , '' Professor Maria Teresa La Porte told CNN . `` We do n't understand . '' `` If they are looking for innocent victims , the place to find them is here , '' she said . `` There is no way to stop them . '' She said it is an open campus with students from various backgrounds -- including Basque -- where people `` can come here completely freely . '' The blast could be heard across the campus of the private school , which has 12,000 students -- including more than 1,000 scholars from countries outside Spain . It is also home to Spain 's top-rated journalism school , which is located not too far from the blast site . A spokeswoman for Clinica Universitaria de Navarra -- located across the street from the university -- said that 24 patients were treated for injuries ranging from glass cuts to hearing problems . Most have been released and only two are expected to remain overnight , she said . Two other patients are being treated at Hospital Virgen del Camino , also in Pamplona , but their nationalities were not clear . Those being treated at Clinica Universitaria de Navarra included 18 Spaniards and six others with the following nationalities : American woman from California , age 20 ; Italian woman , age 28 ; Portuguese woman , age 23 ; Chilean woman , age 25 ; Peruvian man , age 28 and Philippines man , age 34 . Thursday 's explosion came just days after Spanish police arrested four suspected ETA members early Tuesday . Authorities accused them of forming a terrorist cell that was ready to attack , the Spanish Interior Ministry said in a statement . Three of the suspects were arrested in or near the city of Pamplona , in Spain 's northern Navarra region , which has Basque roots and was to be the base for the alleged cell , the statement said . The fourth suspect was arrested in the city of Valencia , on Spain 's eastern coast . Police seized two revolvers and ammunition ; various timers that might be used for bombs ; detonating cord ; items that might be used to make a bomb attached to the underside of vehicles ; various substances that might be used to make explosives ; and computer documentation , the ministry said . All four suspects -- three men and a woman -- were born in Pamplona and range in age from 26 to 29 , the ministry said . ETA is blamed for more than 800 killings in its four-decade-long fight for Basque independence . The European Union and the United States list ETA as a terrorist group . CNN Madrid Correspondent Al Goodman contributed to this report .
Car bomb blast at the University of Navarra in Pamplona , Spain Thursday . NEW : 27 people injured , none seriously , hospital tells CNN . Blast days after arrests of four suspected members of separatist group ETA . Authorities accused them of forming a terrorist cell that was ready to attack .