US Deputy Secretary of State William Burns called on the PM pic.twitter.com/SOjAcK0PV9 — PMO India (@PMOIndia) July 11, 2014

NEW DELHI: Extending a formal invitation to Prime Minister Narendra Modi for a visit to the US, President Barack Obama has expressed keenness to work closely with him to make the bilateral relations a "defining partnership" in the 21st century.Thanking Obama for the invitation, Modi said he looks forward to a result-oriented visit in September with "concrete outcomes" that impart "new momentum and energy" to the strategic partnership.Obama's letter of invitation was handed over to Modi by deputy secretary of state William Burns when he called on him here.In his letter, Obama reiterated his invitation to Modi to visit Washington in September and to work closely with him to make India-US relations a "defining partnership" for the 21st century, a PMO statement said on Friday.While receiving the letter, Modi said he looked forward to a "result-oriented visit with concrete outcomes that impart new momentum and energy to India-US strategic partnership", the statement said.The Prime Minister was of the view that re-energising the partnership between India and the US would send an important message to the region and beyond.Articulating his vision for India-US relations, Modi said that the relationship between the world's oldest and largest democracies should not only be for the benefit of the two countries, but "should emerge as a powerful force of good for peace, stability and prosperity in the world".