Ukraine on Thursday demanded for a "just punishment" over a seven-month-old invasion sending shock waves around the world amid Russia biggest conscription since World War II.
Ukraine had also urged the United Nations to create a special tribunal and strip Moscow of its UN Security Council veto power as a diplomatic showdown loomed in New York.
President Volodymyr Zelenskiy told world leaders at the annual UN General Assembly on Wednesday that "a crime has been committed against Ukraine, and we demand just punishment.''
Earlier, President Vladimir Putin's order to mobilise another 300,000 Russians to fight, signaling a major escalation of a war.
The war between Ukraine and Russia has already killed thousands, displaced millions, pulverised cities, damaged the global economy and revived Cold War confrontation.
The conscription campaign may be the riskiest domestic move of Putin's two decades in power, after Kremlin promises that it would not happen and a string of battlefield failures in Ukraine.
Monitoring group OVD-Info said nearly 1,400 people in 38 Russian cities were detained in anti-war protests on Wednesday.
Independent news outlets said some of those arrested were served summons to report to military enlistment offices on Thursday, the first full day of conscription.
Flights out of Russia has also been selling out after Putin's announcement.
"Every normal person is (concerned), it's horrible," said one man, identifying himself only as Sergey, disembarking in Belgrade after a flight from Moscow.
"It is ok to be afraid of the war and such thing," the man added.
The Security Council has been unable to take meaningful action on Ukraine because Russia is a permanent veto-wielding member along with the United States, France, Britain, and China.