BAGHDAD, June 1 — The number of unidentified corpses discovered in Baghdad soared more than 70 percent during May, according to new statistics from the Iraqi Ministry of Interior, an indication that sectarian killings are rising sharply as militias return to the streets after lying low during the first few months of the troop “surge.”

In May, 726 unidentified bodies were found in Baghdad, many bound and shot in the head or showing signs of torture and execution, compared with 411 during April, according to figures provided by a ministry official who spoke on the condition of anonymity because he was not authorized to release the information.

The Bush administration and military have cited a decline in sectarian killings as proof that the troop escalation is working. And despite May’s increase in corpses, the numbers remain far below the peak of sectarian executions last year. In July and August, for example, a total of 5,106 people died violent deaths in Baghdad alone, according to the United Nations, including 3,391 reported by the city’s morgue.

The new figures also show a decline in the number of deaths of identifiable victims in Baghdad to 344 in May from 495 in April. While victims of car bombs, homemade bombs and mortar strikes can usually be identified, those who are kidnapped, tortured and executed are normally stripped of identification before their bodies are dumped.