Philippine President Rodrigo Duterte’s arbitrary deadline to defeat ISIS-affiliated fighters in the southern city of Marawi quietly passed Monday with victory nowhere in sight, setting off fresh concerns that the emerging Filipino terror group is stronger than advertised.

Duterte had aimed for the army, fighting with technical support from U.S. advisers, to clear the Islamist forces from Marawi by Monday after three weeks of fierce fighting that has forced most of the 200,000 residents to flee from the city.

Military spokesman Brigadier General Restituto Padilla said Tuesday that the progress had been slower than expected, as around 100 militants (made up of local and foreign fighters) sheltered in built-up downtown precincts, offering fierce pockets of resistance and using locals as human shields. He could not give an estimate of when the battle, which has involved bombing raids from the Philippines air force, would be won.

This isn’t the first time the government’s deadlines to win back the city have proved overly optimistic. Duterte set a three day deadline earlier in June, when the military initially estimated it would take just a week to clear militants from the city.

ISIS mock the army

As the battle enters its fourth week, military officials have also conceded that the militants control more of the city than previously thought. Lieutenant General Carlito Galvez told Reuters the fighters had control of 20 percent of Marawi — twice the estimate given by the military the previous week.

ISIS has crowed over the Philippine military’s inability to dislodge them from the city. In a statement issued through their propaganda arm, Amaq, the group said the army had “completely failed,” and claimed to have killed 200 government soldiers while holding two-thirds of the city.

The government has dismissed this claim, saying 58 security forces, 26 civilians and more than 200 militants have been killed in the fighting so far.

The slow progress against the group comes despite confirmation that the Philippine military is now fighting with technical support from U.S. forces. The Pentagon, which regularly rotates dozens of special forces troops through the south of the country for military exercises, said it was providing the Philippines with security assistance and training in intelligence, reconnaissance and surveillance. A U.S. P-3 Orion surveillance plane has been spotted over Marawi, and U.S. forces have been photographed flying surveillance drones over the city.

Duterte admitted Sunday that the battle was more serious than he had anticipated, and said that ISIS’s leader, Abu Bakr al-Baghdadi, had specifically ordered the attack.

Ongoing battle

The crisis erupted on May 23, when militants from the ISIS-affiliated Maute clan rampaged through Marawi, after the army raided the local hideout of Isnilon Hapilon, the leader of ISIS-affiliated militant group Abu Sayyaf. Hapilon was reportedly appointed emir of all ISIS-aligned forces in the Philippines by al-Baghdadi.

In response, Duterte declared martial law over the entire southern island of Mindanao, where Marawi is located. The Philippines is predominantly Catholic, but the southern third of the country is home to a large Muslim minority, and for decades the government has fought multiple rebel groups seeking a separate Islamic state in the south.

Rohan Gunaratna, head of Singapore’s International Centre for Political Violence and Terrorism Research, told VICE News that by demonstrating they could capture and hold territory, the ISIS-affiliated militants were seeking to bolster their credentials as a fully-fledged province of the Islamic State.