MANILA - (3RD UPDATE) Gunmen ambushed the mayor and vice-mayor of Balaoan, La Union Wednesday, killing the latter.

Vice Mayor Alfred Concepcion and his daughter Mayor Aleli Concepcion were on their way to the city hall here when the suspects opened fire on their vehicle.

The elder Concepcion died from multiple gunshot wounds, police said. Mayor Aleli was wounded in the attack.

Their bodyguard Mike Ulep was also declared dead on arrival by physicians.

Both Concepcions were running for re-election in next year's midterm polls.

Some 150 bullet shells were found at the crime scene, said investigators.

Director General Oscar Albayalde, Philippine National Police chief, said initial reports show that the two officials have not received any threat prior to Wednesday's ambush.

Police are also looking at politics as a possible motive for the ambush as well as the possibility that a private armed group was hired for the attack, Albayalde added.

"We are looking into the possibilities of also political motivation dito dahil sa mukhang mainit 'yung laban doon sa probinsya," he told reporters Wednesday.

A special investigative task group has also been formed to look into the attack.

Malacañang denounced the recent attack and expressed condolences to the Concepcion family.

"The Palace strongly denounces the recent ambush against Balaoan, La Union Mayor Aleli Concepcion and her father, Vice Mayor Alfred Concepcion," Presidential Spokesperson Salvador Panelo said in a statement.

"We pursue and prosecute the persons behind these brazen murders and bring them to justice," he added.

At least 17 other mayors and vice mayors have been killed by shadowy assailants or law enforcers since President Rodrigo Duterte assumed office:

1. Vice Mayor Aaron Sampaga of Pamplona town, Cagayan - August 5, 2016

2. Mayor Samsudin Dimaukom of Datu Saudi Ampatuan town, Maguindanao - October 28, 2016

3. Mayor Rolando Espinosa of Albuera town, Leyte - November 5, 2016

4. Vice Mayor Anwar Sindatuk of Datu Saudi-Ampatuan town, Maguindanao - November 27, 2016

5. Mayor Mohammad Limbona of Pantar town, Lanao del Norte - December 30, 2016

6. Mayor Arsenio Agustin of Marcos town, Ilocos Norte - June 3, 2017

7. Mayor Joven Hidalgo of Balete town, Batangas - June 10, 2017

8. Mayor Reynaldo Parojinog of Ozamiz City, Misamis Occidental - July 30, 2017

9. Vice Mayor Jackson Dy of Roxas town, Oriental Mindoro - September 23, 2017

10. Vice Mayor Jonah John Ungab of Ronda town, Cebu - February 19, 2018

11. Mayor Ronald Tirol of Buenavista town, Bohol - May 27, 2018

12. Mayor Antonio Halili of Tanauan City, Batangas - July 2, 2018

13. Mayor Ferdinand Bote of General Tinio town, Nueva Ecija - July 3, 2018

14. Vice Mayor Alex Lubigan of Trece Martires town, Cavite - July 7, 2018

15. Vice Mayor Al-Rashid Mohammad Ali of Sapa-Sapa town, Tawi-Tawi - July 11, 2018

16. Mayor Mariano Blanco III of Ronda town, Cebu - September 5, 2018

17. Mayor Alexander Buquing of Sudipen, La Union - October 1, 2018

-Report from Micaella Ilao and Raffy Santos, ABS-CBN News