Outgoing Indian Ambassador to the US Harsh Vardhan Shringla called on President Donald Trump at the Oval Office of the White House before leaving the country and thanked him for strengthening the Indian-American relationship.

It is probably for the first time that a US President has met an outgoing Indian Ambassador, which experts say is reflection of the significance Trump attaches to the India-US partnership.

"Amb Harsh Shringla, who is proceeding to New Delhi to take up his assignment as Foreign Secretary, called on Trump at Oval Office of the White House and thanked him for his steadfast support for strengthening the India-US strategic partnership," the Indian Embassy in Washington DC said in a tweet on Sunday.

Shringla, 57, is scheduled to take up the next assignment as India's Foreign Secretary on January 29.

Shringla, who arrived in the US on January 9, 2019, and presented his credentials to Trump at the White House two days later on January 11, played a key role in bringing the India-US relationship back on track, especially in the second half of the year.

"I give Harsh Shringla great credit for his tireless pursuit in taking the India-US relations to a new dimension by prudently navigating the highly partisan and complicated US political arena called the US Congress. That's what I would call a real Champion Diplomat," New York-based Al Mason, who is an expert on global real estate investment and education, said after attending the farewell that Shringla hosted at his India House on Friday.

"He has been one of the most charismatic, persuasive and result-oriented diplomat representing India in the US. He has spent each hour of his tenure in pursuit of building the most solid bridge between India and the US," Mason said.

Before taking Dubai-bound Emirates flight from the Dallas International airport Sunday morning, Shringla tweeted, "A final goodbye", along with his pictures, one in the lawns of India House – the official residence – and another at the entrance of the Indian Embassy in downtown Washington DC.

"All the best to my colleague," tweeted Emily Haber, the German Ambassador to the US.

In a lighter tone, she said her counterpart in New Delhi, Walter J Lindner, "is looking forward to meeting you and to giving you a ride in his bright red Hindustan Ambassador!". Haber posted a picture of the Red Ambassador too.

"Dare say this red Ambassador looks better than the iconic Volkswagen Beatle," commented India's Deputy Ambassador to the US Amit Kumar.

"Bon Voyage & best wishes to Amb Shringla as he moves to Delhi for his next imp (ortant) assignment. It has been a privilege to work closely with him these past few months to advance & consolidate the India-US Strategic Partnership," Kumar tweeted.  "Bitter sweet moments in Washington this evening wishing. Ambassador Shringla adieu from the US but knowing that he will be shepherding us from Delhi," tweeted Sandeep Chakravorty, the Indian Consul General in New York.

Envoys of several diplomatic missions, including those from neighbouring nations and African countries, had attended Shringla's farewell, reflecting his popularity in the Washington's diplomatic community.

Before leaving the country, Shringla met top US Congressional leaders, including House of Representatives Majority Leader Steny Hoyer and thanked him "for his understanding and support" of India-US relations. He also called on Secretary of State Mike Pompeo.

"Saying farewell isn't easy, especially when it's to a valued partner & friend," tweeted Acting Assistant Secretary of State for South and Central Asia Alice G Wells."It's been a pleasure working with you to make US India relationship the strongest it's ever been. Congrats on FS appointment & looking forward to continuing our partnership," she said on the eve of Shringla's departure.

Shringla, 57, is scheduled to take up the new assignment on January 29.