"The United States is deeply concerned that Lashkar-e-Taiba (LeT) leader Hafiz Saeed has been released from house arrest in Pakistan," Nauert said adding that the country's government should make sure that he was arrested and charged for his crimes.
LeT is a terrorist organization responsible for killing hundreds of civilians, including American citizens, in terrorist attacks, Nauert said.
Pakistan's court decided to end Saeed's house arrest earlier this week, as the country's government had failed to provide convincing arguments as it wanted to extend the arrest for three months. Saeed had been under house arrest since January and after the release, he delivered a provocative speech concerning India in Lahore.
Pakistan's refusal to take action against Saeed as well as his free movement around the country has been one the biggest stumbling blocks in Pakistani-Indian relations.
Since 2012, the United States, for its part, has offered a $10 million reward for any information that brings Saeed to justice.
The group is believed to be behind the deadly Mumbai bombings in 2008 that left 166 dead and 300 others wounded in India's most populous city.