Washington/New Delhi, May 23 (IANS) : US President Barack Obama congratulated Manmohan Singh Saturday, a day after he was sworn in as India's prime minister for a second term, and the two leaders resolved to work together on global challenges, including terrorism.

In their telephonic conversation, Obama said he looked forward to continuity in the India-US strategic partnership, a key aide to the prime minister said in New Delhi.

Obama also congratulated India on "successfully completing the largest democratic exercise that the world has ever seen", terming it "a testament to the strength of India's democracy", a White House statement said.

"The two leaders recalled their warm meeting in London on April 2 (during the G20 summit) and discussed their mutual desire to strengthen US-India relations and work together to address common global challenges, such as the economic downturn, climate change, and counterterrorism," the statement added.

Obama also invited the prime minister to visit Washington, it said.

Manmohan Singh too reiterated his invitation to Michelle and Barack Obama to visit India, the Indian official said.