"The language used by the Prime Minister against a chief minister of a state was uncharacteristically sharp and is a matter of concern," Singh said here.
"There was nothing illuminating about what he said. A prime minister must not single out chief minister of a state and subject him to criticism," said Singh.
The former Union minister was commenting on the Prime Minister's attack on Gujarat Chief Minister Modi yesterday when Singh had said it would be disastrous for the country to have him as the prime minister.