In the latest incident on Monday three gunmen flagged down and killed a candidate for the city council in southern Cotabato while he travelling with his two young children, police said.
In an effort to crackdown on violence, authorities have imposed a nationwide gun ban and set up checkpoints to arrest violators.
Leonardo Espina, a police spokesman, said on Tuesday that operations to disarm nearly 100 private armies on the payroll of political warlords were still ongoing.
Election violence has become the main concern in the run-up to the May vote, particularly after last November's massacre in the southern province of Maguindanao.
Some 57 people were killed in what is believed to have been the Philippines' deadliest single case of political violence.
About 130 people were killed during the last elections in 2007.
|The next 90 days will see candidates holding rallies across the country [AFP]
Both leading candidates in the presidential race have promised to bring clean government and a fresh start for the Philippines after nine years of scandal-tainted rule by the incumsbent, Gloria Macapagal Arroyo.
A recent opinion poll showed Aquino and Villar neck-and-neck, but analysts say it is too early to establish a two-horse race because voters have yet to hear detailed policies from them.
The Pulse Asia independent survey last month pointed to a tight race showing the two being statistically tied with 37 per cent for Aquino and 35 per cent for Villar. The margin of error was plus or minus 2 percentage points.
Arroyo, who took office in 2001, is barred from running again.
Allegations that she stole the 2004 presidential elections, and that her husband profited from a multi-million-dollar telecoms contract and other deals have marred her rule.
Two other candidates, Gilberto Teodoro, the former defence chief, and Joseph Estrada, the former president, could both pull a surprise and improve their ratings.
The Pulse Asia survey showed Estrada's rating at 12 per cent while Teodoro's stood at 4 per cent.
The start of the official poll campaign is also expected to level the playing field for candidates due to an election law putting a campaign spending cap of about 500 million pesos ($11m) for presidential candidates, or 10 pesos per voter.
During the campaign period candidates are expected to sing and dance on makeshift stages along with movie and TV personalities at political rallies across the archipelago of 7,100 islands before revealing their campaign promises.
Ronald Holmes, political science professor and president of Pulse Asia Inc, said dramatic changes in voters' preferences can be expected during the campaign period.
"It's still very fluid because most voters have not really absorbed the candidates' messages," he said, adding that poverty, corruption, unemployment and high prices of basic commodities are among the main issues that resonate with the electorate.