"We applaud the Indian people for turning out to vote in historic numbers and the government of India for their exceptional execution of this massive undertaking," she said in a statement. "India's elections are the largest exercise in democracy in human history."
According to the Election Commission, 67.1 percent of India's 900 million voters voted. In contrast, only 55.5 percent of Americans turned up at the polling stations in 2016.
Looking ahead to Modi's second term, Ortagus said that Washington was confident that the relations between the two countries centered around the US Indo-Pacific strategy will continue on an "upward trajectory".
"We look forward to working with the newly elected government on a range of important issues, including expanding economic and energy ties, enhancing defence and security cooperation, countering the threat of terrorism, and enhanced collaboration in space," she said.
"We are confident that the strong and upward trajectory of our partnership will continue.
"The United States and India enjoy a strong strategic partnership that stands on a foundation of shared values, extensive people-to-people ties and a commitment to a secure and prosperous Indo-Pacific region," she added.
Ortagus told reporters: "We're confident in the fairness and the integrity of the Indian elections."
(Arul Louis can be reached at arul.l@.in and followed on Twitter @arulouis)
( With inputs from IANS )