BAGHDAD, Sept. 1 — Newly released statistics for Iraqi civilian deaths in August reflect the strikingly mixed security picture that has emerged from a gradual six-month increase in American troop strength here: the number of deaths across the country rose by about 20 percent since July, but in the capital itself, the number dropped sharply.

The figures, provided by Iraqi Interior Ministry officials on Saturday, mirrored the geographic pattern of the troop increase, which is focused on Baghdad. The national rise in mortality is partly a result of the enormous death toll, more than 500, in a truck bomb attack that struck a Yazidi community in August north of the capital, outside the areas directly affected by the additional troops.

As Ryan C. Crocker, the American ambassador to Iraq, and Gen. David H. Petraeus, the top commander of military forces here, prepare to brief Congress on the progress of the troop increase, Iraqi politicians, clearly recognizing what is at stake, view the new figures through the lens of how their parties hope that Congress will assess the situation in Iraq.

“We were hoping the figures would go down, but what happened was expected,” said Haidar al-Ebadi, who sits in Parliament as a senior member of Prime Minister Nuri Kamal al-Maliki’s Dawa Party. The troop increase made it harder for insurgent groups to operate in Baghdad, he said, so they pushed outward to easier targets.