Baghdad, Iraq ? Sunni insurgents are striking back with attention-grabbing bombings in Baghdad and gruesome killings posted on the Internet, in an apparent effort to shore up their positions around the Iraqi capital as the U.S. struggles to secure the city.

That is changing the nature of the conflict in Iraq, at least temporarily – shifting the main focus from the Sunni-Shiite “civil war” of recent months to a renewed attention on Sunni insurgents as the root of the crisis.

The shift could be temporary if Shiite death squads once again become active in Baghdad. But for now, the change indicates how all sides opposed to the U.S. presence show surprising resilience and ability to switch strategies to survive.

As the Shiite militias have faded from view, Sunnis have accelerated their attacks. Lt. Gen. Ray Odierno, the No. 2 commander in Iraq, said recently that Sunnis were accounting for about 70 percent of the attacks against coalition troops.

“It’s their answer to the ‘surge’ strategy – recoil, redeploy and spoil,” Peter Harling of the International Crisis Group said of the Sunni insurgents. “The strategy is to deploy into the vacuum left by the current focus on Baghdad.”

Inside Baghdad, the insurgent goal appears to be to kill enough Shiite civilians to provoke the Shiite militias, especially the Mahdi Army of cleric Muqtada al-Sadr, back into the streets. That would force a showdown between the Mahdi Army and the Americans, weakening the Shiite militia and straining relations between the Shiite-led government its U.S. backers.

Outside the capital, Sunni militants are trying to expand footholds to the northeast in Diyala province while hitting back hard against a U.S.-backed Sunni tribal militia in Anbar to the west. And a double suicide attack that killed more than 100 Shiite pilgrims in Hillah shows that Sunni extremists also are capable of delivering blows south of Baghdad.

The trappings of an Islamic shadow state with al-Qaida as its base are already taking shape in some towns and cities of Anbar where a government presence hardly exists, according to Sunni residents.

Members of the self-styled “Islamic State of Iraq,” which was proclaimed in October, sometimes flog men in public for “un-Islamic” behavior such as wearing their hair too long. In towns north of Baghdad, the Islamic State has posted signs warning that alcohol and cigarettes are against Islam.

Meanwhile in Baghdad, Sunni insurgents are trying to turn to their advantage one notable early success of the security operation – the virtual disappearance from the streets of armed fighters from the Mahdi militia.

Under tremendous U.S. pressure, Iraq’s Shiite prime minister persuaded al-Sadr to rein in his militia and allow the Americans and the mostly Shiite Iraqi security forces to deploy to protect civilians.

On Sunday, in the most visible sign of that deal so far, hundreds of American and Iraqi soldiers rolled into the Mahdi Army’s stronghold of Sadr City without firing a shot, establishing their biggest presence in the sprawling slum since 2004.

With the Mahdi Army off the streets, Baghdad has seen a sharp drop in the number of sectarian reprisal killings, which had left dozens of bullet-riddled bodies scattered across the capital each day for the past five months.

Indeed, many Shiites believe that the absence of Mahdi protection also has given Sunni extremists an opportunity to stage deadly attacks against them, such as the suicide bombing in Baghdad’s center on Monday.

Al-Sadr has already complained that the security plan has failed to stop the Sunni bombings – a veiled warning that his militia may return to the streets if the Americans and their Iraqi partners cannot restore order.

The gruesome slaughter of 18 policemen in Diyala province appeared aimed at telling Iraqis that they cannot count on the government to protect them. Last weekend, an al-Qaida-affiliated group posted an online video showing the policemen kneeling as masked gunmen fired into the back of the captives’ heads.