Several petrol bombs and grenades have exploded at a political rally in Kenya, killing at least five people and injuring 82 others, officials say.

The blasts took place in the capital Nairobi late Sunday as hundreds of people were demonstrating against a draft constitution that has triggered widespread protests in the country, Associated Press reported.

Kenyans are due to vote on a new constitution on August 4.

Meanwhile, Kenyan Prime Minister Raila Odinga confirmed that at least three people have lost their lives and 79 have been wounded, adding that a criminal investigation has been launched to probe the incident and determine who was behind the attack.

“10 of the patients are in serious conditions and another four have been rushed to a Nairobi Hospital bringing the total number to 82,” a hospital official said.

Several high-ranking members of the Kenyan parliament also took part in the rally.

The controversial draft includes reforms to rein in rampant corruption in the country and also an abortion clause, fiercely opposed by Christians, that allows a health expert to terminate pregnancy if a mother’s health is at risk.