Ferguson, Missouri (CNN) -- President Barack Obama spoke with Missouri Gov. Jay Nixon on Thursday, sharing his concerns about recent violence in Ferguson after the shooting of unarmed teenager Michael Brown by a police officer.
"Now's the time for healing, now's the time for peace and calm on the streets of Ferguson," Obama told reporters.
Nixon, for his part, said he would be making changes to help change the tone in the community, but he did not say what they would be. But he said it was crucial to allow protesters to express their anger so long as they respect the rights of others.
"We will not get the healing that we all need if the only response from the public is, 'Y'all just be quiet,' " he said.
Nixon traveled to Ferguson to appeal for calm after a night in which heavily armed police and protesters clashed. Wednesday's violence was the fourth straight night of unrest after Brown's shooting Saturday.
Nixon said he would visit the St. Louis suburb amid calls for continued protests and rising anger among residents about a lack of progress in the case and the treatment of protesters.
Police have also received harsh words from national media organizations after the brief arrest Wednesday of two reporters and the tear-gassing of an Al Jazeera America camera crew.
The worsening situation in Ferguson is deeply troubling, and does not represent who we are as Missourians or as Americans," Nixon said in a statement Thursday. "While we all respect the solemn responsibility of our law enforcement officers to protect the public, we must also safeguard the rights of Missourians to peaceably assemble and the rights of the press to report on matters of public concern."
Nixon's statement comes after a fourth night of violent clashes between police and protesters that began Sunday with unrest and looting in the city on St. Louis' northern border.
After ordering protesters and reporters to turn off their cameras, police fired smoke bombs, tear gas and rubber bullets at protesters after some threw objects at them Wednesday, according to media accounts. CNN crews have not been ordered to turn off their cameras during the protests.
Twelve people were arrested, Ferguson police Chief Thomas Jackson said. Two officers were injured.
History of trouble
While locals say race relations have long been troubled between the city's mostly African-American population and the mostly white police force, anger spilled out after Brown's shooting death.
Police have released few details of what happened but have said the officer, whose identity has not yet been made public by officials, was defending himself against an effort by Brown to grab his weapon.
Jackson said the officer was sent to a hospital for treatment of facial swelling after the incident, but he did not say how he received the wounds.