Troops in the Philippines are using attack helicopters to battle Islamist militants who have seized parts of a southern Philippine city.
A military spokesman said “surgical air strikes” were targeting about 30-40 militants in the city of Marawi.
The violence erupted after a failed army raid to capture a top militant leader. Gunmen are said to have taken hostages and freed prison inmates.
Thousands of people are reported to have fled the city.
Marawi is a mainly Muslim city in Lanao del Sur province on the southern island of Mindanao. The province is a stronghold for the Maute group, which has pledged allegiance to the so-called Islamic State (IS) militant group.
On Tuesday, Philippine troops tried to capture Isnilon Hapilon, a leader of the Abu Sayyaf militant group who has also pledged allegiance to IS. He is on a US terror watchlist.
But the raid failed and dozens of gunmen came out on to the streets of Marawi, reportedly flying IS flags.
At least 20 people, including 13 militants and five soldiers, are reported to have been killed in subsequent fighting.
About a dozen hostages are also reported to have been taken from a church and troops say they are investigating reports of civilian deaths.
The militants have also freed more than 100 inmates from two prisons. Reports said gunfire and explosions could be heard across the city, and some buildings had been set on fire.
“The military is conducting precise, surgical operations to flush them out,” said military spokesman Jo-Ar Herrera. “The situation is very fluid and movements are dynamic because we wanted to out-step and out-manoeuvre them.”
Duterte, the controversial ‘strongman’ of the Philippines
Philippines country profile
Philippine President Rodrigo Duterte imposed martial law in Mindanao on Tuesday in response to the violence, and cut short a visit to Russia.
Martial law allows the use of the military to enforce order and the detention of people without charge for long periods.
This is only the second time martial law has been declared since the fall in 1986 of President Ferdinand Marcos.