State Department Spokesperson Heather Nauert said: "The two leaders affirmed the strong US-India strategic partnership and India's status as a major defence partner of the US."
Meeting on the sidelines of the G20 ministerial meeting in the Argentine capital, they also discussed the agenda for the forthcoming 2+2 Ministerial Dialogue, that will bring together India's External Affairs Minister Sushma Swaraj, Defence Minister Nirmala Sitharaman, Secretary of State Mike Pompeo and Defence Secretary James Mattis, she said.
The dialogue of the cabinet officials for foreign affairs and defence from both countries. was to have taken place in Washington last, but was postponed after President Donald Trump forced the resignation of Rex Tillerson as secretary of state in March.
No new dates have been set for the meeting.
Ms Nauert said that Mr Singh and Mr Sullivan also discussed "opportunities to advance stability in Afghanistan and the region" where Trump assigned a role for India in helping deal with Afghanistan.
"We want them to help us more with Afghanistan, especially in the area of economic assistance and development," he said while outlining his policy for Afghanistan.
Ms Nauert's statement made no mention of North Korea.
Mr Singh met Vice President Kim Yong Dae, Foreign Minister Ri Yong Ho and Culture Minister Pak Chun Nam during the two-day visit.
In Buenos Aires, Singh also met Argentina's President Mauricio Macri and Foreign Minister Jorge Faurie, according to a tweet by an official for the president's G20 office.
Group of Twenty - or G20 - brings together 19 developed and developing countries and the European Union to discuss economic issues.
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