Baghdad ? A sniper felled a U.S. soldier in the tough Arab Jabour district south of Baghdad. His compatriots charged for a house where they thought the gunman was holed up.

One stepped on a buried, pressure-triggered bomb at the house. That soldier and three others died and four more were wounded in the blast.

The five soldiers were assigned to Maj. Gen. Rick Lynch’s Task Force Marne. He said the sophisticated attack that killed his forces Saturday was a new tactic and the work of al-Qaida in Iraq.

“As we surged, the enemy surged,” Lynch told The Associated Press in a telephone interview Sunday. “We do indeed make safety and security our first priority, but we are not going to stop taking the fight to the enemy.”

Lynch said al-Qaida in Iraq had operated freely in the area before his troops flooded the region as part of the six-month-old American drive to calm Baghdad and central Iraq.

With the deaths, at least 3,690 members of the U.S. military have died since the Iraq war started in March 2003, according to an Associated Press count.

Iraq’s most senior Sunni politician, meanwhile, issued a desperate appeal Sunday for Arab nations to help stop what he called an “unprecedented genocide campaign” by Shiite militias armed, trained and controlled by Iran.

Adnan al-Dulaimi said “Persians” and “Safawis,” Sunni terms for Iranian Shiites, were on the brink of total control in Baghdad and soon would threaten Sunni Arab regimes which predominate in the Mideast.

“It is a war that has started in Baghdad and they will not stop there but will expand it to all Arab lands,” al-Dulaimi said in an impassioned e-mail to the AP.

Sunni Arab regimes throughout the Middle East fear the growing influence of Iran’s Shiite theocracy with radical groups like Hezbollah and Hamas as well as the Syrian regime.

But his fears of a Shiite takeover of Baghdad were not as far-fetched. Mahdi Army militiamen have cleansed entire neighborhoods of Sunni residents and seized Sunni mosques. Day by day, hundreds have been killed and thousands have fled their homes, seeking safety in the shrinking number of majority Sunni districts.

Al-Dulaimi resorted to the extremely harsh language a day after Prime Minister Nouri al-Maliki, a Shiite, returned from his second visit to Tehran since taking power 14 months ago.

And he castigated fellow Sunnis in the Middle East, saying they “did not make any move and did not even bother to denounce what is taking place against your brothers at the hands of Iranian militias and death squads.”