U.S. President Barack Obama on Saturday called outgoing Indian Prime Minister Manmohan Singh to thank him for his role in boosting bilateral ties.

Singh, who has served as premier for the past 10 years, offered to resign earlier in the day after the ruling Congress Party was routed in the general elections by the main opposition Bharatiya Janata Party (BJP).

Singh, also a well-known economist, is likely to remain as the caretaker premier until BJP's Narendra Modi, who led the opposition to victory Friday, is sworn in next week to succeed him.

In his phone conversation with Singh, Obama expressed his gratitude for Singh's "critical role in transforming and deepening the U.S.-India strategic partnership and our cooperation on global challenges," the White House said in a statement.

Obama also said he "looked forward to further expanding the strong relationship between the United States and India with Prime Minister-elect Narendra Modi," the White House added.

Obama spoke to Modi over the phone Friday and invited him to the White House.

Bilateral ties were strained after the U.S. arrest of Devyani Khobragade, India's deputy consul general in New York, in December over visa fraud charges, escalated into a major diplomatic row.