MANILA - President Rodrigo Duterte on Tuesday said he is rejecting calls for him to sack Transportation Secretary Arthur Tugade amid the slew of glitches encountered by the Metro Rail Transit (MRT-3) system.

“I will not do that. I have to trust in Tugade that he can correct the mistakes there, if there are, and fix it,” Duterte told reporters in a chance interview in Taguig City.

Tugade earlier said he served at the pleasure of the President after an administration critic, Magdalo party-list Rep. Gary Alejano, called for his resignation amid problems hounding the MRT-3, Metro Manila’s busiest but ill-maintained rapid transit system.

Alejano's call came days after an MRT coach detached from the train between the Ayala and Buendia stations, forcing commuters to walk on the tracks.

The President on Saturday apologized for the inconvenience caused by the incident, which occurred about a week after the government terminated the maintenance contract of Busan Universal Rail Inc. and took over the railway's upkeep.

Transportation Undersecretary for Railways Cesar Chavez had said the National Bureau of Investigation (NBI) would look into the incident, which could be an attempt to sabotage MRT operations.

Tugade refrained from commenting on the investigation, saying he did not want to preempt the NBI.

The NBI was called in to look into possible "human negligence" while the MRT would investigate the technical aspect of the incident, said the train system's spokesperson Mike Capati.

"Our MRT trains are safe. We're trying our best to maintain our trains," he said, adding there was no offloading of passengers over the weekend.

The MRT runs the length of EDSA and ferries over 500,000 people a day.

• Stop MRT operations? Consider riding public, says Palace