Baghdad ? Four more U.S. troops and a British soldier have died in attacks, military officials said Tuesday, in a possible sign that extremists are regrouping after a drop in American deaths last month.

The spate of recent U.S. deaths – 19 so far in August – seems certain to intensify the debate over U.S. progress to calm Iraq and gain ground against militants ahead of a key September report to Congress.

U.S. deaths had dropped slightly in July to 79 – the lowest monthly tally since 70 were killed in November. Before July, more than 100 American forces died each month in the April-to-June period as the U.S. military struck out at insurgents on dangerous streets and cities across Iraq.

But U.S. commanders say rogue Shiite militias have stepped into the gap left as Sunni insurgents have been pushed back, and are now responsible for most attacks on Americans in Baghdad and surrounding districts. Such a trend would elevate fears that Iraqi forces are not yet able to maintain security even when insurgents are beaten back. Large numbers of Iraqi police are believed to have allegiances to Shiite militia groups.

The spike in deaths comes as the overall number of U.S. troops in Iraq has temporarily peaked at its all-time high – nearly 162,000 – as new units arrive to replace those on the way out, the Pentagon said.

U.S. officials also have warned that militants might try for spectacular attacks before the September report – expected to be a high-level military and diplomatic assessment on U.S. strategies in Iraq and what’s needed in the months ahead.

Leery of that, Baghdad officials tightened checkpoints and announced plans for curfews and vehicle bans ahead of a mass Shiite religious march planned later this week in the capital.

Thousands of Shiite pilgrims began walking from the country’s south and gathering from elsewhere for the march.

Shiite pilgrimages often have been the target of devastating attacks by Sunni insurgents. But some of the devout, like Sami Faraj, a 52-year-old government employee, said they would march nevertheless.

“We do not care about the bombings and the terrorists. We are ready to sacrifice ourselves for the cause and for the sake of the prophet’s descendants,” Faraj said.