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.

Although violence has dropped by more than 80 percent around Iraq and particularly Baghdad, the U.S. military has repeatedly said the improved security conditions remain fragile.

Iraq assumes control over much of the country on Jan. 1 under a security pact that replaces an expiring U.N. mandate.