Republic of Congo's interior minister says that four people have been killed in clashes between police and demonstrators against a constitutional reform that could see the country's longtime president eligible for a new term.

Raymond Zephirin Mboulou said Wednesday that three people were killed in Brazzaville and another in Pointe-Noire Tuesday. He said seven people were injured and police arrested 16.

Demonstrators attacked police stations and burned tires. Police fired tear gas to disperse protesters.

Politicians campaigning against the Oct. 25 referendum had called for a campaign of "civil disobedience" to begin Tuesday.

Under current laws 71-year-old President Denis Sassou N'Guesso is barred from seeking re-election when his second term expires next year. The referendum calls for scrapping a two-term limit and 70-year-old age limit for candidates.