MANILA, Philippines?Buluan Vice Mayor Ismael "Toto" Mangudadatu on Wednesday accused the Ampatuans of being behind the murder of a relative of a key witness in the Maguindanao massacre.

Doc Uling, cousin of Ampatuan town vice mayor Rasul Sangki, was shot dead by unidentified gunmen Tueday. Sangki was the first witness to implicate Datu Unsay Mayor Andal Ampatuan Jr. in the massacre of 57 people in Maguindanao last November 23.

The gunmen also opened fire at the residence of Sangki's uncle, Mohammad, a day after Sangki told the court on January 13 that he saw relatives and supporters of Mangudadatu being hauled away at gunpoint after their convoy was ambushed.

Sangki said Ampatuan had even informed him four days before the massacre of a plan to block the convoy as Mangudadatu's supporters travelled to register him as a candidate to run against Ampatuan in the race to become Maguindanao governor in May elections.

Mangudadatu said the attacks were meant to sow fear and force the witnesses in the gruesome murders to recant their statements against the Ampatuans.

"These are clearly intended to frighten the witnesses thinking some of them will withdraw their statements,? he said.

But Mangudadatu said the latest attacks would not stop him from pursuing his fight against the Ampatuan clan.

Ampatuan has pleaded not guilty to multiple counts of murder over the November attack that stunned the nation and raised questions about the influence of the Ampatuan clan in President Gloria Macapagal-Arroyo's government.

The Amptuan patriarch, Andal Sr., and several other clan members were also arrested after martial law was briefly imposed in Maguindanao and charged with rebellion. No date for their court appearance has been set. With a report from Agence France-Presse