Myanmar army artillery shelled positions held by civilian militias in a northwestern town for a second day on Friday, rebel fighters and a lawmaker said, after the ruling junta declared martial law there to quell a local rebellion against its rule. The junta said martial law was imposed in Mindat in Chin State late on Thursday after whom it called "armed terrorists" attacked a police station and a bank. The attacks posed a further challenge to the military as it struggles to restore order in the country amid widespread anger over its coup in February which ousted the elected civilian government of Aung San Suu Kyi. The resistance has expanded in recent weeks from daily street protests and strikes to attacks on junta-appointed administrators and ambushes of security forces by civilians. The newly-formed Chinland Defence Forces on Friday said it was behind the fighting in Mindat. It ambushed a convoy of military reinforcements on Friday, according to one fighter and a local legislator. "Fighting is still ongoing and Tatmadaw is firing into Mindat town using artillery," said the lawmaker, referring to the military by its local name. He requested that he remain anonymous. "This is the most serious fighting." The Chin rebels numbered about 400-500, who between them had about 30-40 assault rifles, plus traditional hunting rifles, he said. "But they are not trained well," he said, adding most had only a week-long training session. A spokesman for the Chinland Defence Force declined to provide details on the fighting, citing security reasons. LOSING CONTROL "They (the junta) can no longer rule the city except in some areas where they have bases. They have no control in the rural areas," the spokesman said. One of its fighters told Reuters six trucks were seized and many weapons taken. A military spokesman did not answer calls from Reuters. The state-run Myanmar News Agency said the fighting on Wednesday and Thursday in Mindat involved 100 people who attacked a police station and about 50 targeting the state-run Myanmar Economic Bank. Security forces had repelled the attack without suffering casualties, it said. The Chin lawmaker said the fighting erupted after the military refused to release seven local youths wrongly detained by authorities. He said five local militia fighters had been killed. News website Irrawaddy said two had died, citing one of the fighters. Pro-democracy groups and ethnic minority armies have been rallying behind a National Unity Government (NUG) that is seeking domestic and international support to undermine the military as prevent it from consolidating power. The NUG earlier this month announced the formation of a People"s Defence Force, to protect civilians from the military. Some fighters have sought training with insurgents that have battled the Tatmadaw for decades in border regions. So far, 788 people have been killed in the military"s crackdown according to an advocacy group. The military, which disputes that number, imposes tight restrictions on media, information and the internet. Reuters cannot independently verify arrests and casualty numbers. In a sign of the continued defiance, pictures and video on social media showed demonstrators marching in the commercial capital Yangon on Friday chanting "we believe that we gonna win, we must win, we must win". Others carried signs saying "coup must fail".