Initial reports identified the victim as Jose Doton, secretary general of the Bayan Muna-Pangasinan chapter. His brother Diosdado, who was driving the motorcycle, survived the ambush.
Doton was killed two days after a Bayan Muna coordinator was shot dead in San Fernando, Pampanga.
Doton is also the chairman of "Timuyog Ti Mannalon A Mangwayawaya Ti Agno" (TIMMAWA), a group that opposed the construction of San Roque Dam in this province.
The victim was also the regional coordinator of the militant Alyansang Magbubukid ng Gitnang Luzon (AMGL) and the provincial head of the Bagong Alyansang Makabayan (Bayan) of the province.
Pangasinan police director Senior Superintendent Alan Purisima said the 62-year-old militant leader was riding in a motorcycle along with his brother when they were waylaid by unidentified gunmen waiting for them in Barangay Camanggaan in this town.
Doton died instantaneously from a gunshot wound to the head, police said.
According to Bayan regional chairman Roman Polintan, it was only last February that the vice chairman of their group, Nicanor Serpio, was gunned down.
Last Sunday, Manuel Nardo, coordinator of Bayan Muna in Barangay Quebiawan in San Fernando City was shot dead.
Polintan claimed the murders of Doton and Nardo both "bore the trademark of the notorious death squads" said to be behind the murders of at least 52 militants last year and another 27 so far this year.
Bayan issued a statement claiming Doton was the 67th member of their organization killed this year.
The group also accused the government of "duplicity in the move to investigate rising political killings."
Polintan said President Arroyo’s order to solve the spate of killings was merely prompted by "raging public opinion."
"Instead of pursuing leads pointing to military involvement in these killings, the President and her Cabinet are trying to divert the issue by injecting the idea of so-called communist purges," Polintan said. He also chided Senior Superintendent Samuel Pagdilao for clearing the military and police forces of involvement even before an investigation has been completed.
He said such statements reflect the Arroyo administration’s bias in favor of its security forces.
Other militant groups have singled out the Philippine Army’s 7th Infantry Division chief, Maj. Gen. Jovito Palparan, as masterminding the killings, abductions and grave human rights violations in Central Luzon.
Polintan said any investigation of the killings "should be undertaken by disinterested people of proven integrity and probity."
The communist New People’s Army (NPA) rejected government allegations that they were behind a string of killings of leftist activists, insisting that military-backed death squads were to blame.
Amnesty International earlier scored the rising number of leftist murders in the country.
Malacañang said anyone suspected of involvement in the killings should be investigated and charged, even those from the government.
"We do not want people to say the cases are being neglected. Let the ax fall where it will. Whoever committed the crime must be punished. But it is also not right to accuse anybody without basis," Executive Secretary Eduardo Ermita said.
Presidential Adviser on the Peace Process Jesus Dureza, for his part, expressed his concern over the killings of leftist leaders and called it "anathema to our democratic system."
"I am getting worried that some sectors are getting fascinated by extra-judicial executions," Dureza said.
A former military man himself, Ermita said he was used to being blamed for every crime committed against groups and personalities identified with the left.
"They always point at government forces as the ones responsible but they can hardly prove it. And that is why it is impossible for them to say there is a pattern," he said.
Ermita it is also possible that the communists are purging their own ranks.
National Security Adviser Norberto Gonzales maintained the NPA appeared to be behind the killings.
Gonzales suggested the killings were part of a bloody internal purge to cleanse guerrilla ranks of suspected military spies.
In a related development, the military said they had uncovered mass graves in Misamis Oriental.
According to Brig. Gen. Cardozo Luna, commanding general of Army’s 4th Infantry Division based in Cagayan de Oro City, skeletal remains were discovered in Barangay Kibungkod, San Fernando, Bukidnon while more mass graves were found in Region 10.
Among those allegedly executed by communist rebels under a certain NPA commander Nonong Salusad were civilians suspected of spying for the military.
Gonzales earlier claimed one grave was located in Bukidnon but he did not specify the exact location.
Gonzales said a team from Cagayan de Oro City discovered the bodies of some 20 people in one barangay who were reportedly liquidated by the rebels in a span of several months.
He said the graves were uncovered following interviews with relatives of slain leftist militants.
Gonzales added another mass grave was discovered in Tarlac where he will lead an investigation to verify the reports.
Gonzales said some of the victims’ family members expressed willingness to stand as witnesses once the government files charges against suspected communist leaders responsible for the killings.
He theorized that the purges began in 2003 under the Communist Party of the Philippines and the NPA.
Gonzales maintained that neither the Armed Forces of the Philippines (AFP) nor the Philippine National Police (PNP) had anything to do with the killings.
He said authorities began to suspect a purge following the "pattern" of killings of militant leaders in the past few months.
The CPP-NPA undertook a similar bloody purge in the 1980s dubbed "Operation Zombie" and "Kampanyang Ahos."
The purges resulted in the torture and deaths of thousands of rebels, including women and children who were relatives of suspected deep penetration agents. - With Cesar Ramirez, Ding Cervantes, Aurea Calica, Katherine Adraneda, Jaime Laude, Lino de la Cruz, Charlie Lagasca, AFP