Clashes between Fano militiamen and the Ethiopian National Defence Force (ENDF) continued over the weekend. Residents of Gondar, Amhara's second-biggest city, said that heavy weapons fire that began on Sunday could be heard into Monday morning.
Temesgen Tiruneh, director general of Ethiopia's national intelligence service who was appointed to oversee enforcement of the state of emergency, acknowledged that militia fighters had taken some towns and districts.
"This robbery force is operating with the goal and intention of overthrowing the regional government by force and then advancing to the federal system," Temesgen said in comments broadcast late on Sunday by state-affiliated Fana Broadcasting.
The fresh unrest in Africa's second-most populous country comes just nine months after the end of a devastating two-year war in the neighboring region of Tigray which also drew in fighters from Amhara.
The government said Saturday that authorities had arrested people connected to "the security crisis in Amhara" after imposing a state of emergency on the northern region following clashes between local fighters and federal troops.
On Friday, it said that the emergency measures would cover Amhara "for six months" but could be imposed "nationwide in relation to any situation or movement that aggravates the security problem."
Tensions have been rising since April when the federal government announced it was dismantling regional forces across Ethiopia, triggering protests by Amhara nationalists who said the move would weaken their region.
Clashes in Amhara have escalated in recent weeks, prompting travel warnings from foreign governments and the grounding of flights, with Prime Minister Abiy Ahmed's office saying emergency measures were needed "to control this unacceptable movement."
The government communications service said those who "exacerbate the security crisis... (and engage in) various acts of destruction have been arrested," without giving details about the number of detainees or the timing of the arrests.
According to the emergency decree, anyone found violating its provisions could face "imprisonment of between three to ten years."
The decree also allows for suspects to be searched and held without a warrant.
Local fighters from Amhara's Fano militia have taken control of three towns in the region, residents told AFP over the weekend.
According to residents of Lalibela, a UNESCO World Heritage site famous for its 12th and 13th century rock-cut churches, Fano fighters took over the town and its airport earlier this week.
The Ethiopian Human Rights Commission said last week that civilians had been attacked, with damage reported to property, while transport services and internet had been suspended in some areas of Amhara.
National carrier Ethiopian Airlines has cancelled flights to Dessie, Lalibela and Gondar.
The United States has "expressed concern" about the violence, while Britain and Spain have both warned their citizens against traveling to parts of Amhara.
Information for this report came from Reuters and AFP.