Baghdad ? For the second time in less than a week, U.S. forces were drawn into deadly fighting against insurgents — a reminder of the ongoing dangers American forces face well after President Barack Obama declared a formal end to combat.

With a persistent insurgency, ongoing sectarian tensions and no agreement on a new government after six months of wrangling, stabilizing Iraq before all American forces leave still seems a distant dream.

Wednesday’s raid, in which at least six people were killed, was in the former insurgent stronghold of Fallujah — highlighting the persistent danger that al-Qaida-linked militants still pose despite years of efforts by both Iraqi and U.S. forces to root them out.

Insurgents seem to have redoubled their efforts this summer to target Iraqi security forces taking over from the departing Americans — nine Iraqi soldiers died Wednesday in a roadside bombing while two police officers in Baghdad were shot and killed. The militants are trying to undermine the so-called “Sons of Iraq” — the anti-al-Qaida militia that was instrumental in reducing violence.

The anger with which Fallujah officials reacted to the raid — conducted by Iraqi troops from Baghdad instead of local forces — spotlights another persistent threat to Iraq’s security: deep divisions between the minority Sunnis in places like Fallujah and the Shiite majority that rules the country.

Details of the raid were murky. U.S. officials described it as an Iraq-led mission targeting al-Qaida-linked militants with Americans in an advisory capacity. Officials in Anbar province railed against the raid, calling it a heavy-handed attack that left civilians dead.