NEW DELHI, March 19 (Xinhua) -- The death toll in last Sunday's forest fire in the southern state of Tamil Nadu has risen to 17, with three more critically injured trekkers succumbing to their burn injuries in the hospital in the past 24 hours, police said Monday.

The massive fire broke out last Sunday evening when a group of nearly 40 people, mostly college students, went trekking in Kurangini hills in Tamil Nadu's Theni district, some 540 kms from state capital Chennai.

While 10 people -- seven women and three men -- initially died in the fire, 30 others were rescued by Indian Air Force. "Of those rescued, some sustained severe burns. Seven of them have so far died during treatment at a government hospital," a senior police official said.

Cops have already arrested a 30-year-old tour guide in connection with the fire. "The tour guide led the trekking group to the forest. He is being interrogated. Preliminary probe suggests that the group did not obtain required permission from authorities," he said.

A probe is going on to ascertain the cause of the fire, the official said. "We will try to fix responsibility as soon as the investigation is over. Anyone guilty will not be spared," he added.

Forest fires are uncommon in India.