Two men were shot in the head in Myitkyina, capital of Myanmar's northernmost Kachin State when security forces opened fire at a crowd of hundreds of protesters, while the third was shot in the chest in Phyarpon, a small town in the country's southwestern Ayeyarwady Region.
In the second such large-scale strike since the Feb 1 coup, at least nine labor unions from various sectors such as construction, manufacturing and agriculture called for the massive mobilization, shutting many businesses and factories.
On Sunday night, security forces took control of hospitals and universities in the largest city Yangon and elsewhere. State media said they acted at the request of people who want stability restored.
Also Sunday, several hundred protesters were arrested, including over 100 people in Yangon, as security forces sought to quell protests, according to local media.
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Physicians for Human Rights, a U.S.-based nongovernmental organization, issued a statement saying it is "appalled by this latest wave of violence by the Myanmar military, including the invasion and occupation of public hospitals and wanton excessive force against civilians."
The group called for foreign governments to put further pressure on Myanmar's military, saying actions taken by the international community so far are "clearly insufficient" to stop human rights violations in the country.
The takeover of the hospitals is seen by some people as a way for security forces to more easily detain injured protesters after they are transported to hospitals to receive medical treatment.
From Monday morning, workers and other protesters marched in the streets of such major cities as Yangon and Mandalay, according to local media. Most banks remained closed even though Myanmar's central bank had urged them to resume operations.
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More than 50 people have been killed by the security forces since the military seized power. It has insisted that it is using minimal force against protesters to keep order.
Besides restoration of civilian rule, the protesters are calling for the release of their elected leaders, including Aung San Suu Kyi, who remain detained after the military ousted the government led by her National League for Democracy party.