NEW DELHI/WASHINGTON: Prime Minister Narendra Modi had extended an invitation to US President Donald Trump to visit India at his convenience but no formal or written invite was sent to him, official sources said Wednesday.The clarification by the sources came two days after a White House spokesperson said Trump was honoured by Modi's invitation to be Chief Guest of India's Republic Day but is unable to participate due to scheduling constraints."We have noted the statement made by the White House about the visit of US President Donald Trump to India. It may be recalled that during the visit of Prime Minister to the US in June 2017, he had extended an invitation to President Trump to visit India at his convenience," said a source.The source further said "no formal or written invitation was extended as it is a normal practice between two countries to make informal enquiries before extending a formal invitation."The source said high-level exchanges are important element of India-US strategic partnership and both sides continue to be engaged with each other to find a mutually convenient date and occasion for the visit.Modi had invited Trump for a bilateral visit to India during their talks in Washington last year.They are scheduled to attend the G-20 Summit in Argentina on November 30 and December 1. It is possible that the two leaders might meet and discuss bilateral relationship there.Every year, India invites world leaders to attend its Republic Day celebrations.In 2015, the then US president Barack Obama had attended it as the chief guest which was his second visit to India as American president.This year, leaders from 10 ASEAN countries had attended the Republic Day celebrations.In 2016, the then French president Francois Hollande was the chief guest of the parade while Japanese Prime Minister Shinzo Abe was the chief guest at the celebrations in 2014.The heads of state and government who have attended the Republic Day celebrations include Nicolas Sarkozy, Vladimir Putin, Nelson Mandela, John Major, Mohammed Khatami and Jacques Chirac.