Over 100 kg of explosive was suspected to have been used in the terror attack at the Indian embassy in Kabul on Monday, in which the lone bomber had made a failed attempt to gain entry into the complex, officials said on Wednesday.

In the wake of the attack, Indian officials have held a series of meetings with Afghan authorities with regard to the security of the mission and Indians working here.

"The Afghanistan government has offered its utmost cooperation in ensuring proper security at the Embassy," Indian Ambassador Jayant Prasad told PTI.

He said even before the attack, security at the embassy had been stepped up after intelligence inputs warned of a terror strike. Further measures will be taken to strengthen the security, he said.

His comments came as the death toll rose to 58 from 41. The deceased included 17 students, who were on their way to school when the bomb exploded outside the gate of the embassy.

Investigators suspect that nearly 100 kg of explosive was used in the attack as bodies were thrown up to 30-40 metres away because of the impact of the blast, Prasad said.

Prasad said the lives of several other Indian employees of the embassy were saved because of the alertness of Indo Tibetan Border Police jawan Roop Singh as he thwarted the bomber's intention of going inside the complex.

There were at least 15 employees inside the building at that time.

Citing investigations carried out so far, Prasad said the bomber had apparently tried to gain access to the embassy complex to carry out the attack.

This is evident as the hand of an ITBP guard was found clung to the door of the gate though his body was thrown away by several meters, he said.

He said a white Toyota carrying the explosives was just behind the car of Defence Attache Brigadier R D Mehta while the latter was entering the complex.

The bomber apparently wanted to enter the complex along with Mehta's car but Roop Singh got suspicious and did not open the door, the Ambassador said, citing reconstruction of events.

Realising that he had been detected, the bomber panicked and detonated the blast there only, Prasad said.

On measures to strengthen security, he said the team of officials, headed by Secretary (West) in Ministry of External Affairs Nalin Surie, held a series of discussions with the Afghan authorities and have been assured of all help in this regard.