The Philippines set up police and military checkpoints across the country in heightened security measures following a deadly explosion in Davao city, authorities said on Monday.The police have been placed on maximum alert, with increased patrols and checkpoints set up at strategic areas nationwide, after the September 2 blast that killed at least 15 people and wounded dozens of others, Efe news reported.President Rodrigo Duterte, who served as Davao Mayor for 22 years, on Saturday declared a 'state of lawlessness' across the country, although he reassured the public that this did not constitute a declaration of martial law.The President also warned that reprisals could be expected from terrorist group Abu Sayyaf, who claimed responsibility for the attack, according to the Philippine Star newspaper.Several countries, including the US, Britain, Australia, Canada and Singapore, have issued travel warnings, urging citizens to reconsider plans to travel to Mindanao province, where Davao city is located, and take extra safety precautions.