The Indian army has ordered an inquiry into the alleged rape of a young woman by soldiers of the presidential guard.
President Kalam favours "tough measures"
The men, who were arrested earlier this week, belong to an elite unit protecting President Abdul Kalam.
Army Chief General NC Vij has promised the "most stern action" if the accused are found guilty.
Reports say President Kalam has directed Defence Minister George Fernandes to take "tough measures" against the men.
The elite Presidential Body Guard, which consists of cavalry mounted soldiers, has also come under investigation, they say.
The incident, which has made front-page news, has shocked many Indians with experts saying it points to a rot within the highly disciplined army.
"The alleged involvement of members of the military's most show-cased unit, the PBG, is a sad pointer of the state of our military," an expert from the Institute for Defence Studies and Analyses told the AFP news agency.
The incident is alleged to have taken place in a park in the heart of the Indian capital, Delhi, close to the presidential palace.
Senior police official Manoj Lall told the BBC the girl, a student of Delhi University, was in the park with a male companion when the guards allegedly assaulted both of them.
He said one of the soldiers robbed her friend, while two of them raped the girl in the park.
A medical examination established that she was sexually assaulted.
The incident is said to have taken place in the middle of the day.
Apart from guarding the president, army troops are deployed in civilian law and order duty in many sensitive states, including Kashmir and the north-east of the country.
Many soldiers have been accused of human rights violations there, including allegations of rape.