The United Nations Security Council voted unanimously on Saturday night to impose sanctions on Libya’s leader, Col. Muammar el-Qaddafi, and his inner circle of advisers, and called for an international war crimes investigation into “widespread and systemic attacks” against Libyan citizens who have protested against the government over the last two weeks.

The vote, only the second time the Security Council has referred a member state to the International Criminal Court, comes after a week of bloody crackdowns in Libya in which Colonel Qaddafi’s security forces have fired on protesters, killing hundreds.

Also on Saturday, President Obama said that Colonel Qaddafi had lost the legitimacy to rule and should step down. His statement, which the White House said was made during a telephone call with Chancellor Angela Merkel of Germany, was the strongest yet from any American official against Colonel Qaddafi.

The Security Council resolution also imposes an arms embargo against Libya and an international travel ban on 16 Libyan leaders, and freezes the assets of Colonel Qaddafi and members of his family, including four sons and a daughter. Also included in the sanctions were measures against defense and intelligence officials who are believed to have played a role in the violence against civilians in Libya.