A powerful Philippine clan leader suspected of involvement in the massacre of 57 people has been taken into custody, officials said.
Andal Ampatuan Jr had surrendered to authorities, they said. He denies organising the killings, AFP reported.
Earlier, troops and police swooped on towns on the southern island of Mindanao run by the Ampatuan family.
The massacre took place on Monday as a convoy of vehicles used by a rival politician was ambushed.
The group, involved in activities for the 2010 elections, was taken to a remote hill region, shot at close range and their bodies dumped in shallow graves.
Taken by helicopter
Interior Secretary Ronaldo Puno said that Mr Ampatuan Jnr was taken by helicopter from his hometown in the restive Maguindanao province on Thursday morning to a nearby airport.
From there he was being flown to the capital Manila for questioning, Mr Puno said.
Police were reported to have rounded-up and disarmed a 200-member paramilitary force in Maguindanao on Thursday. They also made several arrests.
Map
Officials named militiamen under the control of Mr Ampatuan Jr - the mayor of a town in Maguindanao - as suspects.
All police officers from one town are under investigation for the killing, AFP news agency reported, citing government officials.
Although prominent members of the Ampatuan family are allies of President Gloria Arroyo, they have been expelled from her party since the killings.
President Arroyo, who earlier declared a national day of mourning, has promised that the gunmen would not escape justice.
The BBC's Danny Vincent, in Manila, says the Ampatuans have been involved in a long-standing feud with a rival family who want to oppose them in the national and local elections.
Philippine politician Ismael Mangudadatu has claimed it was gunmen loyal to the Ampatuans who ambushed his supporters as they were travelling to register his name for the polls.
Among the dead were Mr Mangudadatu's wife, his two sisters and several key supporters, as well as at least 13 journalists who were travelling with them to witness his registration as an election candidate.
Analysts say the Ampatuans have effectively been in charge of Maguindanao for decades.
Andal Ampatuan Snr has served in the Philippines Congress and won the governorship of Maguindanao unopposed for several terms.
His son was reportedly planning a similarly unopposed run to replace his father but then Mr Mangudadatu decided to run as well.