Sandhu is currently High Commissioner to Sri Lanka, Ashraf is High Commissioner of Singapore and Kumar is spokesperson of the Ministry in New Delhi.
The transfers, which were due, came at a time when India has been in international news for a slew of major decisions the Modi government took since its reelection for a second term.
The government has drawn flak from the Western media over reorganization of Jammu and Kashmir state, suspension of mobile internet and detention of politic in Kashmir.
Lately, the BJP government has been facing stiff opposition and widespread protests over its Citizenship Amendment Act (CAA) that grants citizenship to the persecuted religious minorities of three Islamic nations in the neighbourhood Bangladesh, Afghanistan and Pakistan.
India's economic slowdown has also been a major concern among its major trading partners in the West.
Official sources said Sandhu will take over as the US Ambassador from Harsh Vardhan Shringla, who just returned to New Delhi. Shringla will take over as Foreign Secretary from Vijay Gokhale, who is retiring later this month.
Sandhu has previously served as deputy chief at the Indian embassy in Washington DC. The government is sending Gopal Baglay, currently in PMO in New Delhi, to Colombo, as a replacement of Sandhu.
Sources said Ashraf will replace ambassador Vinay Kwatra, who is being transferred to Nepal. Kwatra is taking over from Manjeev Singh Puri who has just retired.
A career diplomat, Ashraf has been instrumental in India's strong partnership with Singapore for key development projects at home like smart cities and skill development. He has earlier served in US, Germany and Nepal.
Kumar, who has been the youngest and one of the most effective and popular spokespersons of the Ministry, will take over from Renu Pall, who recently returned to New Delhi. Pall was transferred after an impending investigation against her over allegations of financial irregularities and mismanagement at the mission in Vienna.
( With inputs from IANS )