MANILA — An unattended box triggered a brief bomb scare at the Ayala Bridge in Ermita, Manila on Thursday afternoon.

A concerned citizen reported the 12 by 10-inch box to a traffic enforcer, who called policemen to the area at around 1:40 p.m.

After about 15 minutes, authorities said the box had no explosives or hazardous materials.

It contained used clothes and a dead dog, the Manila Police District said.

The Philippine National Police earlier in the day said it monitored a number of bomb threats sent via email following Sunday’s deadly bombing of a Catholic mass at the Mindanao State University in Marawi.

“Noong isang araw ay sunod-sunod ang bomb threat na naitala natin at yan naman po ay nirespondehan agad ng PNP at nakikiusap tayo sa ating mga kababayan na mag-ingat tayo sa mga tinatanggap na email dahil itong mga bomb threat na ito ay ini-course through the email,” PNP spokesman Col. Jean Fajardo said.

At least four people died and around 50 others were injured in the Marawi bomb attack last weekend.

The blast from an improvised explosive device could have been a revenge attack for government operations against three Islamist militant groups -- Dawlah Islamiyah-Philippines, Abu Sayyaf and Maute -- in western Mindanao in recent days, the military earlier said.

Watch more News on iWantTFC

Watch more News on iWantTFC

— With reports from Robert Mano, ABS-CBN News; Agence France-Presse