BAGHDAD, Iraq (CNN) -- Six U.S. troops were killed in Iraq on Monday, making 2007 the deadliest for the American military in the Iraq war.
The grim record came despite lower death rates in recent months, which were not enough to offset death tolls that topped 100 during three months in the spring.
Four soldiers were killed when a roadside bomb exploded near their vehicle in northern Iraq's Tameem province; another died in combat in Anbar province.
A sailor was killed in Salaheddin province "as a result of injuries sustained from an explosion while conducting operations," the military said.
According to a CNN count of Pentagon figures, 853 U.S. service members have died so far in 2007. The next highest death toll was in 2004, when 849 were killed.
The total number of U.S. military deaths in Iraq stands at 3,856, including seven civilian contractors of the Defense Department.
The high number of deaths this year corresponds with the U.S. troop buildup called the "surge" and a crackdown on insurgents in and near Baghdad.
Monthly death tolls were highest in the first part of the year: 83 deaths in January, 81 in February and 81 in March. Numbers peaked in the next three months, with 104 deaths in April, 126 in May and 101 in June.
The numbers have dropped from that level since -- with 78 in July, 84 in August, 65 in September, 38 in October and 12 so far in November.
Civilian deaths have also dropped in recent months, U.S. and Iraqi authorities say.
The Iraq war began in March of 2003 and in that year there were 486 U.S. military deaths.
In 2004, major offensives were responsible for many fatalities, including the massive operation in Falluja in November and fighting between U.S. troops and Shiite militants in Najaf.
The number of deaths in 2005 was 846 and in 2006 it was 822.
The U.S. military also announced on Tuesday that it intends to release nine detained Iranians in Iraq "in the coming days," a move that dovetails with the American hope that Iranian authorities are honoring a recent pledge to stop Iranian help to insurgents in Iraq.
"These individuals have been assessed to have no continuing value" and don't pose a "further threat" to Iraqi security, said Rear Adm. Gregory Smith. Two of them are from the "Irbil 5" detained in January. Irbil is the largest city in the Kurdish area of Iraq.
The U.S. military had accused the five Iranians arrested in Irbil of having links to Iran's Islamic Revolutionary Guard-Quds Force, a military unit accused of aiding insurgent activity -- including the distribution of roadside bombs.
Smith said Tuesday that materials for roadside bombs "do not appear to have arrived into Iraq after the Iranians have made their pledge to stop arming, funding and training extremists."
"We hope in the coming weeks and months to confirm that Iran has indeed honored its pledge through further verification that the flow of ammunitions and other lethal aid has indeed stopped," said Smith, who noted that Iran, Iraq and the United States plan to hold another round of security talks.
Last month, Gen. David Petraeus, the top-ranking U.S. military official in Iraq, told CNN the Iranian ambassador had given assurances to his Iraqi counterpart that such training and supplying of insurgents would end.
Meanwhile, a Kurdistan Regional Government official on Tuesday confirmed to CNN that two Iranian consulates had been established in the region, offices created in the wake of the arrests in Irbil.
At the time of the arrests, Iran insisted the arrested officials were "diplomats" working in a diplomatic mission, while Iraq's Foreign Ministry and the U.S. military said it was a "liaison" office which did not have diplomatic status.
One of the new consulates is in a building in Irbil that had been closed down during the January raid, the Kurdistan official said.
Also Tuesday, the U.S. military reported that U.S. and Iraqi troops found 22 corpses buried in Iraq's Lake Tharthar region.
The Iraqi Army and local security forces "are investigating the mass grave to determine the identities of the deceased and the causes of death for notification of their families," the military said.
Lake Tharthar is in both Anbar and Salaheddin provinces and northwest of Baghdad.
U.S. and Iraqi troops have been conducting an operation in the same region since Sunday to target al Qaeda in Iraq.
So far, they have found and destroyed two car bomb facilities and a number of weapons caches and detained 30 men.
The military also said that coalition troops on Tuesday killed eight people described as terrorists and detained 10 suspects in operations targeting al Qaeda and foreign militant networks in central and northern Iraq.
The military also said an operation involving Iraqi forces in the Tikrit area on October 30 led to the detention of 39 "suspected insurgents" and the discovery of a torture cell, a mobile hospital, car bombs, rocket-propelled grenades, machine guns and a Katyusha rocket. E-mail to a friend
CNN's Jennifer Deaton contributed to this report.