I asked because most of the people in my country have submitted basic registration form through indian embassy. But the embassy closes the date 14 days before the final submisison date of aiims pg.

The previous session's prospectus doesnt mention anything as such. However let me double check that for you please. 

Yojana, The Govt. of India nominates Foreign Nationals under Self financing foreign candidate and Foreign Candidate under General Cultural scholarship scheme. That might be the reason. I would suggest you to reach out to AIIMS helpdesk but meanwhile complete your Basic registration on your own with one email id and send another application through the Embassy with another Email id so that you dont miss the chance. Because the prospectus doesnt mention any specific procedure for foreign Nationals.