The army has moved to quell mass protests against its rule, killing at least 730 people according to a local monitoring group.
Min Aung Hlaing's invitation to the meeting of the 10-country Association of Southeast Asian Nations has drawn scorn from activists who have urged foreign leaders not to formally recognise the junta.
Moe Zaw Oo, deputy minister of foreign affairs for the parallel "national unity government" -- formed Friday by ousted lawmakers mostly from Suu Kyi's party, as well as ethnic-minority politicians -- said ASEAN had not reached out to them.
"If ASEAN wants to help solve the Myanmar situation, they are not going to achieve anything without consulting and negotiating with the NUG, which is supported by the people and has full legitimacy," he told Voice of America's Burmese service. "It's important that this military council is not recognised. This needs to be handled carefully."
Meanwhile, the junta continued targeting the media on Sunday, arresting Japanese freelance reporter Yuki Kitazumi. He was arrested at his home in Yangon on Sunday evening, his assistant said in a message.
In February, he was beaten up and briefly detained during a crackdown on protesters but was later released.
The number of reporters arrested so far has totalled more than 65 and at least 34 remain in custody, according to monitoring group Reporting ASEAN.
Authorities announced Sunday night on state-run television 20 more celebrities and 20 more doctors would be added to their arrest warrant list of 420 prominent people.
Earlier unrest continued across the country on Sunday, with protesters rallying in Mandalay, Meiktila, Magway and Myingyan, showing support for the national unity government.
At Palaw in the country's south, demonstrators brandished banners that read: "Military dictators should not be allowed to rule. The dictatorship will be uprooted.
Support the national unity government." Young demonstrators also staged motorbike rallies while carrying flags in Hpakant and Sagaing.
The previous night, there were violent clashes in the central gem-producing city of Mogok when security forces cracked down on protesters.
According to an AFP-verified video filmed by a resident, soldiers crouched on a street as their commanding officer shouted that he wanted "deaths". The Assistance Association for Political Prisoners (AAPP) verified two deaths at Mogok.
Much of Myanmar remains under a curfew imposed shortly after the coup, running from 8 pm to 4 am every night.
Late Saturday, a young man was shot and killed in Kyaukme town in northern Shan state while riding his motorbike during the curfew.