BAGHDAD, IRAQ -- Hostile fire has killed more U.S. soldiers and Marines in Iraq in May than during each of the three previous months.

If the trend continues, May will be one of the deadliest months for U.S. troops during the past year.

So far, insurgents have killed 54 American troops in May, including 14 in the last three days. With a week left, the month will likely eclipse all but two others - November and September 2004 - for deaths by hostile fire since June 2004, based on figures tabulated by Iraq Coalition Casualty Count, a group that tracks troop deaths from Department of Defense news releases.

The casualty figures appear to end a trend that started soon after national elections in January, when insurgents seemed to shift from targeting U.S. forces to attacking the nascent Iraqi army and police.

With sectarian violence increasing between the nation's Shiite and Sunni Muslims, the figures raise the question of whether Iraq is turning into two battlefields: one of insurgents vs. the U.S. military and another of Iraqi sects fighting each other.

Since the nation's interim government took office on April 28, more than 590 Iraqis have been killed in attacks, most of them civilians.

"There is going to be a wave of violence (targeting U.S. forces) as long there is occupation," said Amer Hassan Fayadh, a Baghdad University political science professor. At the same time, "when the regime fell, the Iraq state collapsed, too. The replacements for the police were (sectarian) militias."

Those militias, and the groups behind them, have become entangled in a tit-for-tat killing of religious and political leaders as the minority Sunni population, which didn't vote in large numbers during national elections, struggles to find its footing in a nation increasingly dominated by the majority Shiite sect.

With May's figures, though, it's clear that insurgents continue to target U.S. troops, even while fighting rages among Iraqis.

In the months after the elections, the number of insurgent attacks per day plummeted, averaging between the low 30s and mid-40s. They spiked back up this month, hitting an average of about 70 a day before starting to dip during the past couple days.

A Marine offensive this month in Iraq's restive Anbar Province contributed to the U.S. death count. Marines encountered heavy resistance in areas near the Syrian border. Nine Marines were killed and 40 were wounded; at least 125 insurgents were reported killed.

"The insurgents are trying to get back into Fallujah, with little success, but they are operating in and around (nearby) Ramadi and up the Euphrates valley," Marine Lt. Col David Lapan wrote in an e-mail from his base in Fallujah. Soldiers and Marines retook that city in bloody battles with insurgents in November.

Many American military officials have pointed to less-effective roadside and car bombs as proof that a series of captures of top insurgent leaders had weakened the insurgency. But 39 of the 54 soldiers and Marines killed so far this month died as the result of those devices.

Insurgents are also using more sophisticated tactics.

During an unsuccessful raid on an Iraqi police station south of Baghdad on Saturday, for example, soldiers responded to a tip about a possible car bomb. As they arrived at the station, the bomb exploded, and a gun battle with insurgents followed. Investigators also found four unexploded 160 mm artillery rounds rigged with timers, according to a military release.

"There has been at least an appearance of things being more sophisticated, more coordinated," said Lt. Col. Steve Boylan, a top military spokesman in Baghdad. "I'm not sure we've seen anything that links different groups, but there's definitely more sophistication in the execution" of attacks.

Bloodshed has continued despite the arrests of suspected insurgent commanders.

The U.S. military revealed Tuesday that a man alleged to be a top insurgent leader in the western city of Ramadi had been captured the day before. Muhammed Hamadi, military officials said, commanded several insurgent cells responsible for attacks against U.S. and Iraqi forces and was instrumental in a series of kidnappings meant to fund operations. He may be linked to Jordanian terrorist mastermind Abu Musab al-Zarqawi.

The military also announced the capture of Mullah Kamel al-Aswadi, the most wanted insurgent in all of north-central Iraq. Caught by Iraqi soldiers at a checkpoint, al-Aswadi is also suspected of having ties with al-Zarqawi and of funding and training insurgents across the region.

A militant Islamic Web site also revealed, with few details, that al-Zarqawi himself may have been injured.

On the same day, a car bomb killed six people and wounded four in front of a girls' junior high school in Iraq. A national assembly member barely escaped assassination on a highway south of Baghdad; four of her guards were seriously injured. And another national assembly member announced in open session that the northern town of Tal Afar was on the brink of "street wars."

"They go down to the streets and fight each other," said councilman Muhammed Taqi al-Mawla. "You know what will happen if this tragedy continues. It will lead to the death of many innocent people."

Even if al-Zarqawi, the most wanted man in Iraq, were killed, it's difficult to gauge how much of a long-term effect it would have on the insurgency, a diffuse enemy thought to be made up of fighters loyal to former dictator Saddam Hussein's Baath party, domestic jihadists, foreign fighters and criminals, said Boylan, the military spokesman.

"Once we kill or capture him that won't end it. ... We're pretty confident that someone else will step in," Boylan said. "Will it have an effect? Sure. But how much? We don't know."

For more information, see http://icasualties.org/oif/.

© 2005 KR Washington Bureau and wire service sources

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