MYANMAR security forces have arrested 39 people suspected of being behind explosions and arson attacks as well as trying to get military training with an ethnic minority rebel group, media controlled by the junta said on Wednesday.

Since the military seized power on Feb. 1, Myanmar has seen a growing wave of small blasts in cities and towns, some targeting government offices and military facilities.

No group has claimed responsibility but the military has blamed people bent on destabilising the country.

The Global New Light of Myanmar newspaper said security forces had seized 48 "handmade mines", 20 sticks of TNT, detonators, fuses and other material in a raid.

Other explosive material including gun powder had also been found, the newspaper said.

Some suspects had also been arrested for trying to join military training with a rebel group in Kayah State in the east, it said.

A relative of Khant Sithu, who was among the suspects identified by the paper, said on the day of the arrest security forces had searched the house for weapons but not found any.

The family member, who declined to be identified, said Khant Sithu had joined protests initially but stopped after the crackdown by authorities.

Myanmar's army has struggled to impose order since seizing power and detaining elected leader Aung San Suu Kyi and other senior figures in her party, with protests, strikes and a civil disobedience campaign crippling businesses and the bureaucracy.

After facing a brutal crackdown on protests, some pro-democracy supporters have sought military training with some of the ethnic minority forces that have been fighting for greater autonomy for decades from remote border regions.

Rallies and candle lit vigils were held overnight to mark 100 days since the coup including in the commercial hub of Yangon, the central town of Bago, the Irrawaddy river delta, the central region of Sagaing and Mon State in the south, according to media reports and social media posts.

Many demonstrators back a National Unity Government (NUG), an anti-junta coalition that has declared itself Myanmar's legitimate authority. Last week, the NUG announced the formation of a "People's Defence Force".

Security forces have killed 783 people since the coup and 3,859 people are in detention, according to the Association for Political Prisoners monitoring group.

The U.N. human rights office said on Tuesday the military was showing no let-up in its efforts to consolidate power and its human rights violations went far beyond killings.

"It is clear that there needs to be greater international involvement to prevent the human rights situation in Myanmar from deteriorating further," said Rupert Colville, spokesman for the U.N. High Commissioner for Human Rights.

The military said it had to seize power because its complaints of fraud in a November election won by Suu Kyi's party were not addressed by an election commission that deemed the vote fair.