"I pay tributes to our brave soldiers," PM Manmohan Singh said in his condolence message to their families.
A Lt Colonel was among the five army personnel killed yesterday when their 32-member convoy was attacked in the ambush at Gumuruk in the country's troubled Jonglei state.
"There were 200 attackers," UN peacekeeping spokeswoman Josephine Guerrero told news agency AFP. UN leader Ban Ki-moon said the attack could amount to a war crime as he joined the UN Security Council in condemning the ambush.
The soldiers killed yesterday are: Lt Col Mahipal Singh, Naib Subedar Shiv Kumar Pal, Havildar Hira Lal, Havildar Bharat Samsal and Lance Naik Nand Kishor.
India has about 2,200 Indian army personnel in South Sudan. They are in two battalions. One is based in Jonglei and the other is in Malakal, in the Upper Nile, on the border with Sudan.
The South Sudan government has blamed followers of rebel leader David Yau Yau for the ambush. Government forces have been battling the rebels in Jonglei while UN peacekeepers have been patrolling between the two sides.
South Sudan ended decades of civil war with Sudan in 2005 and peacefully formed its own country in 2011. But the south is still plagued by internal violence and shaky relations with Sudan. Leaders in Khartoum, Sudan's capital, deny that they are arming Yau Yau.