FACTBOX: The U.S.-Iraqi Baghdad offensive

(Reuters) - Following are details on a new U.S.-Iraqi crackdown on violence in Baghdad.

OVERVIEW

Since the security plan was formally launched, the U.S. and the Iraqi military say there has been a big drop in sectarian bloodshed overall. But chief U.S. military spokesman Major- General William Caldwell noted on Wednesday car bombings in the capital were not under control. He also said bombers were increasingly using suicide vests, probably because of heightened checks on vehicles. Caldwell said it was premature to declare the operation a "success".

OPERATIONS

Brigadier Qassim Moussawi, an Iraqi military spokesman, said in the first eight days of the operation, U.S. and Iraqi troops had killed 42 known militants and arrested another 246. He said 84 suspected militants had been detained. Five hostages held by kidnappers were freed and 642 displaced families had returned to their homes. The number of victims of sectarian death squads initially fell but the total has begun to rise again. Before the operation, 40-50 bodies were found every day on Baghdad's streets. That dropped to around five a day but rose to 25 on Tuesday, police said.

MILITARY DEVELOPMENTS

In a change from previous, failed offensives, U.S. soldiers are embedding with Iraqi units across Baghdad in what are called joint security stations. Caldwell said an additional four such stations had been set up in the past week, bringing the total operational to 14. Iraqi commanders have talked about setting up 28. The first batch of American reinforcements, a brigade of roughly 2,700 soldiers, has arrived. The lead elements of the next brigade are starting to arrive. Caldwell put total Iraqi and U.S. forces on the ground at 90,000 troops, less than the 110,000 figure given by another U.S. general several days ago.

SADR CITY

Caldwell said military operations were taking place in the teeming Shi'ite slum of Sadr City, stronghold of the Mehdi Army militia of anti-American cleric Moqtada al-Sadr. Residents have not reported any large-scale activities or fighting. Many Mehdi militiamen are lying low and Iraq's president has said Sadr had ordered his commanders to leave the country. At least one joint security station would be set up in Sadr City, Caldwell said.

WHAT HAS MALIKI BEEN DOING?

On Tuesday, Shi'ite Prime Minister Nuri al-Maliki made a rare public foray into Baghdad's violent streets. Iraqiya state television showed Maliki talking to an Iraqi soldier near an armored vehicle in Baghdad. The soldier pointed to an area from where he said insurgents had been firing at security forces.

"Don't just fire back, crush the place where the fire came from," Maliki replied. "Don't treat them with leniency. This is an armored vehicle here, use it."

WHAT IS THE OPERATION'S OBJECTIVE?

The idea is to protect the population, pump money into the economy and get government services functioning. U.S. officers say the security operation will take months to peak, but add that they hope to see concrete results around June or July.