MALACAÑANG will reinforce its security measures following the arrest of alleged Chinese spies supposedly doing surveillance work on the presidential palace, key military and government sites.

Speaking to reporters Thursday, Malacañang Press Officer Claire Castro said the latest in a series of arrests involving Chinese spies was "alarming."

"We will continue and intensify our forces to suppress these alleged spies," Castro said.

"It is truly necessary to have stricter security for the Palace and, of course, the President," she added.

The National Bureau of Investigation (NBI) has arrested two Chinese and three Filipinos for allegedly spying on Malacañang, the military and the police.

The NBI said it acted on the information from the Intelligence Service of the Armed Forces of the Philippines last Feb. 14 about "numerous vehicles equipped with unauthorized International Mobile Subscriber Identity catchers conducting signal intelligence."

It said the vehicles were "frequenting military and police camps, other essential systems, facilities and national government assets within Metro Manila."

"Systems were employed to locate and analyze rogue or unlicensed BTS, unauthorized transmissions and interference sources which yielded positive results," the NBI said.

"A rogue BTS is an unauthorized or malicious base station that impersonates a legitimate cellular tower to intercept, manipulate or disrupt mobile network communications. It is often used for unauthorized surveillance, eavesdropping, data theft and network disruption," it said.

The bureau said the Filipinos claimed "they were instructed to drive through key areas, including Villamor Airbase, Camp Aguinaldo, Malacañang, Camp Crame and the US Embassy, among others," and were paid from P2,500 to P3,000 a day.

President Ferdinand Marcos Jr. believes that China has set up sleeper cells in the Philippines following the arrest of five Chinese for suspected espionage in Palawan last month.

A sleeper cell is a group of people living in secret, waiting to be activated for a specific mission.

Castro said the government would intensify its crackdown on illegal Philippine offshore gaming operators (POGOs) amid the resurgence of scamming operations and new human trafficking schemes that were linked to the industry.

Sen. Risa Hontiveros raised the alarm over the resurgence of POGOs despite their being banned.

"We will coordinate with agencies responsible for pursuing any POGOs that continue to operate without a license," Castro said.

"It is the government's obligation to go after them because they are illegal. You can expect swift action on this matter," she said.