BAGHDAD — A pair of car bombs killed more than two dozen people on Saturday, shattering a recent period of calm and serving as a grim reminder that recent gains remain fragile as Iraq prepares to take over security responsibilities for much of the country.

The attacks included one in the Iraqi capital — the first major attack in more than a week — that killed at least 22 people and injured 54, many of them Shiite pilgrims, when bombs exploded Saturday on a busy road that leads to the revered shrine of Kadhimiya.

The U.S. military has said attacks are down from 180 a day last year to about 10 a day this year. Iraq assumes control over much of the country Thursday under a security pact that replaces an expiring U.N. mandate.