Kigali, Rwanda (CNN) -- Seven people were critically wounded when a grenade exploded in downtown Kigali, a government official said Wednesday.
"Two of them were very small children -- 4 or 5 years old," said Ignatius Kabagambe, the director general for the Ministry of Information.
Earlier, he had told CNN that at least one person was killed but he later retracted that.
Three people were arrested at the scene of the attack, which occurred at the Rubangura Building -- a commercial building in the center of the city in front of which people typically congregate to get taxis, Kabagambe said.
Police and military were blocking the streets surrounding the area; a bleeding man could be seen on the ground.
Kabagambe said he could not confirm reports from witnesses who told CNN that a total of about 20 people were wounded in the explosion.
He added that two similar blasts occurred in February -- 150 meters and 600 meters from the site of Wednesday's blast -- and a third in March at the same site of Wednesday's blast.
Kabagambe blamed anti-government dissidents who have fled the country. But he said the attack would not affect celebrations going on throughout the city to mark President Paul Kagame's reelection on Sunday.
"It was a grenade attack," said police spokesman Eric Kayiranga. "The investigations have begun, but it is too early to put blame."
Journalist Josh Kron and CNN's Ben Brumfield contributed to this story