Power formerly served on President Obama’s National Security Council. She is filling the role formerly occupied by Susan Rice, who is now Obama’s national security adviser. The Senate approved Power's nomination 87-10 last week.

The new ambassador said she would work to reform the United Nations and promote human rights.

Power retweeted a picture from her swearing in with Vice President Biden last week, flanked by her husband Cass Sunstein, a former top administration regulatory official.

The U.S. Ambassador to Israel Dan Shapiro also welcomed Power to the social media network.