Two people who could be responsible for the improvised explosive device left near the United States Embassy in Manila Monday are in police custody.

Chief Superintendent Oscar Albayalde, National Capital Region Police Office director, said the two "persons of interest" have similarities with the facial composite sketch the police released on Tuesday.

He attributed the development which could be a major breakthrough to the information provided by witnesses and their own intelligence operatives.

"We connected the dots and based on the cartographic sketch yesterday we were able to get a lot of information," Albayalde said in an interview over dzMM radio on Wednesday.

He said the two are not suspects yet. "The investigation is still ongoing," he said.

One of these people is Rayson Kilala, also known as Rashid Kilala, 34. Police accosted him at 10:30 am Wednesday at his residence in Barangay Bagumbayan in Bulakan town, Bulacan.

Chief Superintendent Aaron Aquino, Central Luzon regional police director, said Kilala was "brought to the Manila Police District for further investigation." .

The second suspect is from Caloocan City. Albayalde did not reveal the person's identity and other details.

The two are undergoing tactical interrogation at the MPD headquarters in Manila. Albayalde is not discounting the duo belongs to a specific group.

"We will be conducting follow-up operations if they are really responsible," said Albayalde.

An ambulant vendor told police a man who disembarked from a taxicab left the bomb at a trash bin along the southbound lane of Roxas Boulevard, around 100 to 150 meters from the US Embassy.

Philippine National Police Director General Ronald Dela Rosa earlier pointed to the Maute group, a band of terrorists whose members are fighting government forces in Butig town, Lanao del Sur, as the people who could be responsible.

"The Maute group is now experiencing casualties in Lanao.. We can theorize it's a diversion," he said in a news conference last Monday. Emmanuel Tupas/DMS