LONDON — In a surprise move, Pakistan’s government on Wednesday sharply revised downward its official estimate of civilian casualties caused by American drone strikes in the tribal belt, highlighting again the contentious nature of statistics about the covert C.I.A. campaign.

The Ministry of Defense released figures to lawmakers saying that 67 civilians were among 2,227 people killed in 317 drone strikes since 2008. The remainder of those killed were Islamist militants, the ministry said.

The figures represented a civilian casualty rate of about 3 percent, falling far below earlier estimates from independent groups — and other government departments — that reported a rate of 6 percent and higher over the same period.

Recently, a United Nations special rapporteur on human rights and counterterrorism, Ben Emmerson, said that the Pakistani government had reported at least 400 civilian deaths since the drone campaign started in 2004.