Officials called the attack a politically motivated massacre. Many of the victims were beheaded, their remains buried in shallow graves. The victims -- at least 13 of them women -- reportedly included a dozen local journalists covering the filing that marked the start of the Philippines election season. Twenty-one bodies were recovered late Monday with three more early Tuesday. Police are looking for more than a dozen other victims. No group has claimed responsibility for the attack in a region known for decades of bloody clashes between Islamic militants seeking autonomy in this predominantly Roman Catholic nation. But authorities indicated that Monday's violence on the south island of Mindanao might be the work of political warlords and gangs who wage war against one another with well-equipped private armies. 'This is a gruesome massacre of civilians unequaled in recent history,' said Jesus Dureza, a provincial official. 'There must be a total stop to this senseless violence and carnage.' Ismael Mangudadatu, the candidate for provincial governor, was not in the convoy at the time of the attack. He told officials that his wife, Genalyn, called him by mobile phone moments before she and her entourage were abducted. She said 100 men had surrounded the convoy, officials said. Then the line went dead. Mangudadatu, deputy mayor of the town of Buluan and a political rival of the current governor of Maguindanao province, had received death threats in recent weeks, officials said. General Leonardo Espina, Philippine National Police spokesman, said Tuesday that officials believe forces connected to the Ampatuan family, which has held power here since 2001, were responsible for the carnage. Elections are traditionally violent here, especially in the southern provinces. On May 14, more than 45 million Filipinos will go to the polls to choose among 87,000 candidates vying for 17,000 national and local positions -- including 268 House seats. The convoy was reportedly carrying more than 40 political activists and journalists riding in several vans when it was hijacked near the town of Ampatuan, said Army Col. Jonathan Ponce, a spokesman for the 6th Infantry Division. The bodies were later found about three miles away. 'Many of them (were) beheaded, including probably journalists,' Ponce said. 'Troops are in the area and tracking down those responsible in these killings.' In a statement, Philippine President Gloria Macapagal Arroyo condemned the violence. 'Civilized society has no place for this kind of violence,' she said. 'No effort will be spared to bring justice to the victims and hold the perpetrators accountable to the full limit of the law.' Eid Kabalu, a leader of the country's largest Muslim rebel group, the Moro Islamic Liberation Front, called the attacks 'gruesome.' Late Monday, the Philippines National Press Club criticized what officials called the withholding of information by authorities on the fate of the journalists. 'We were shocked and grieved to hear what happened to our colleagues,' said Benny Antiporda, the club's president. He said the group would hold a candlelight vigil Tuesday evening at the headquarters of the National Police and the Armed Forces to protest what he suggested was government stonewalling. 'We appeal to the police, the military, the public officials to forget their friendships and other relationships with others and give priority to the search for justice for our brothers,' Antiporda said. Human-rights activists said more than half a dozen journalists are killed each year in political and religious violence in the Philippines. 'The Philippines is a very dangerous place for reporters, especially in the south,' said Vincent Brossel, head of the Asia desk for the Paris-based Reporters Without Borders. 'There is a large culture of violence, nepotism and impunity to law and order. There are influential rich and powerful people who do whatever they want. But if this number is confirmed, it will be the biggest slaughter in this country in many years.' Philippines deputy presidential adviser Lorelei Fajardo said authorities 'should immediately identify whoever are responsible for this, in order for the government to show the people that we will not allow this kind of violence.' Special correspondent Jacinto, based in Mindanao, reported from Zamboanga City and staff writer Glionna from Seoul, South Korea. Special correspondent Sol Vanzi also contributed to this report. 