Bomb in car kills two policemen in northern Mexico MEXICO CITY (Reuters) - An explosive device blew up a car in the northern Mexican city of Ciudad Victoria on Tuesday, killing two policemen and injuring another four in an attack that bore the hallmarks of drug cartels, police said. The improvised bomb, two days after a presidential election, was revenge for recent arrests of gang members, the attorney general's office for Tamaulipas state said in a news release. It went off shortly after midnight outside the home of the Tamaulipas security secretary, where the policemen stood guard, the release said. Army bomb experts had sealed the scene and were determining the type of explosive materials used. The device had been packed into a Ford Focus that had been parked outside for several days and was likely set off by a cell phone, local media reported. There has been a wave of recent attacks using improvised explosive devices in cars in northeast Mexico, where the Zetas cartel battle rivals for control of drug trafficking routes to the United States. On Friday, a bomb blew up a pickup truck in the border city of Nuevo Laredo, injuring seven people but causing no deaths. There has been very little TV footage or photos of the incidents because of attacks and threats on journalists in the region. On Sunday, Enrique Pena Nieto won Mexico's presidential election to replace Felipe Calderon, who has waged a five-and-a-half-year offensive against drug gangs. Calderon was barred by the constitution from running for a second term, but the candidate for his National Action Party, Josefina Vazquez Mota, finished in third place, with dissatisfaction over the drug war cited as a reason for her poor turnout. Pena Nieto of the Institutional Revolutionary Party (PRI) takes office in January and has promised to continue fighting drug cartels but said he will focus on reducing homicides, extortion and kidnapping. Reporting By Ioan Grillo and Lizbeth Diaz; Editing by Daniel Trotta and Sandra Maler