BAGHDAD, Iraq — Dozens of Iraqis were killed yesterday in attacks that included a massive car bombing in Diyala province, where security had improved significantly in recent months.

A car bomb in that province’s capital, Baqubah, killed at least 35 people and injured 66, the American military said in a statement. Iraqi officials provided a higher death toll, saying that 43 had been killed and that women and children were among those killed. The explosions destroyed three buses and damaged 10 shops, the military said.

Meanwhile, in Ramadi, 60 miles west of Baghdad, a suicide bomber killed at least 10 people, according to Iraqi officials.

The car bomb exploded near the provincial courthouse in central Baqubah, a spokesman for a military center staffed by Iraqi and American military personnel, Colonel Ali Jassem, said.

Colonel Jassem said the bombing was “the most devastating attack to have taken place in Diyala since 2003,” and he noted that the bombers managed to penetrate a heavily secured part of the city, which is about 35 miles northeast of Baghdad.

A doctor at a Baqubah hospital, Jassem Muhsin Alwan, said more than 85 people were being treated there. “Many families are still coming around looking for their sons,” he said.

In a statement condemning the attacks, the American military said they “have the appearance of having been carried out by al-Qaida Iraq.”

The attacks occurred in provinces where Iraqi and American military officials have in recent years won hard-fought victories against Sunni insurgents. Security has improved considerably in both provinces in recent months.

“Although attacks such as today’s event are tragic, it is not indicative of the overall security situation in Baqubah,” an American military spokesman in Diyala, Major Mike Garcia, said. “This is the first suicide attack inside Baqubah in almost 90 days, and the overall violence in the city has decreased by 80% since June.”

In Ramadi, at least 10 people were killed when a suicide bomber detonated explosives inside a restaurant, according to a police commander, Tariq Yousif al-Asal al-Dulaimi.

“University students and policemen usually attend this restaurant,” he said.