"We repeat our calls for the military to relinquish power, restore democratically elected government, release those detained and lift all telecommunication restrictions and to refrain from violence," said Price.
The United Nations also expressed "strong concern" over the violence.
"The use of disproportionate force against demonstrators is unacceptable," said Ola Almgren, the UN resident co-ordinator in Myanmar.
Meanwhile, the EU's foreign policy chief said the bloc could impose sanctions on Myanmar's military and was "reviewing" all options.
Raid on Suu Kyi's offices
The US and UN's concern followed a raid by the military on the Yangon headquarters of outsted leader Aung San Suu Kyi's party late on Tuesday.
"The military dictator raided and destroyed NLD headquarters at around 9.30 p.m.," said the National League for Democracy, Suu Kyi's party.
Another day of protest
Earlier in the day, security forces in Myanmar used rubber bullets and tear gas against anti-coup protesters who rallied to defy a ban on gatherings.
Demonstrators want power restored to the deposed civilian government and freedom for the nation's elected leader, Suu Kyi, and her allies.
In pictures: Protests spread in Myanmar over coup
A week after a military coup there, Myanmar is seeing nationwide protests. A broad coalition of doctors, teachers and blue-collar workers is demanding the release of Aung San Suu Kyi and the restoration of democracy.
Image: AFP/Getty Images
Doctors and nurses on the frontline
Less than 24 hours after the coup, doctors and nurses from many state hospitals announced that they were going on strike. They also called on others to join a campaign of civil disobedience.
Image: REUTERS
Broad coalition
Since then, students, teachers, blue-collar workers and many other social groups have joined the protests. The demonstrators sing and chant slogans such as "Give power back to the people!" or " Our goal is to get democracy!"
Image: Ye Aung Thu/AFP/Getty Images
Monks support the protests
Buddhist monks are also among the demonstrators. The "sangha," the monastic community, has always played an important role in this predominantly Buddhist country.
Image: AP Photo/picture alliance
Nationwide protests
Demonstrations are taking place not just in the big urban centers of Yangon and Mandalay — people are also taking to the street in ethnic minority regions, as here in Shan State.
Image: AFP/Getty Images
Three-finger greeting
As in Thailand, the demonstrators have adopted as their symbol the three-finger greeting from the Hollywood blockbuster "The Hunger Games."
Image: REUTERS
Encouragement from the balcony
Many people who are not actively demonstrating themselves applaud the demonstrators and support them by providing them with food and water.
Image: REUTERS
NLD leadership arrested
The demonstrators are demanding a return to democratic government and the release of Aung San Suu Kyi (seen here in The Hague in December 2019) and other high-ranking politicians of the de facto governing party, the National League for Democracy. The military arrested Aung San Suu Kyi and other NLD members on Monday.
Image: Sem Van Der Wal/ANP/AFP/Getty Images
Support for the military government
Supporters of the military government and the generals' proxy party, the USDP (Union Solidarity and Development Party), have also held a few isolated rallies around the country.
Image: Thet Aung/AFP/Getty Images
Memories of the 1988 coup
The coup of 1988 is constantly on people's minds during the current protests. Back then, public order collapsed amid anti-government protests and was restored by the military with the utmost severity. Thousands of people died, tens of thousands were arrested, and many students and activists fled abroad.
Image: ullstein bild-Heritage Images/Alain Evrard
Water cannon in Naypyitaw
The capital, Naypyitaw , in the remote center of the country, was purpose-built by the military and unveiled in 2005. Security forces here have deployed water cannon against the demonstrators.
Image: Social Media via Reuters
Tense situation
The violence threatened to escalate in Myawaddy, a town in southern Kayin State, on Sunday evening. Police deployed tear gas and rubber bullets.
Image: Reuters TV
Flowers for the security forces
On Monday evening, the military announced that the people did not tolerate "lawless troublemakers" and that these must be removed. The demonstrators responded to this threat by giving police officers flowers.
Image: Ye Aung Thu/AFP/Getty Images
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On February 1, army commander Min Aung Hlaing seized power in Myanmar. Coup leaders cited alleged irregularities in a November election that saw the NLD win in a vote the electoral commission said was fair.
Suu Kyi was detained the same day and has not been seen since.
