WASHINGTON, April 25, 2005 (AFP) - Iraqi insurgents have shown improved coordination and greater tactical sophistication in a new surge of attacks following a sharp decline after national elections in January, US defense officials said.

The increased violence comes amid a stalemate over the formation of a new Iraqi government, which US officials worry is dissipating an opportunity opened by the January 30 elections to undercut Sunni support for the insurgency.

"It's not over. Nobody thinks this is over," said a senior defense official, who asked not to be identified.

Attacks fell from about 90 a day before the elections to about 40 a day for several weeks after the vote, Pentagon officials said. But then about two weeks ago the number of attacks rose to about 50 a day.

More significant than the number of attacks is that the insurgent attacks are better coordinated than in the past and more sophisticated, said the senior defense official.

Moreover, he said, members of the former regime have been re-establishing links with foreign fighters led by militants such as Abu Musab al Zarqawi.

He said there was "a definite coincidence of interests" between the two.

Defense officials point to several coordinated attacks involving unusually large numbers of insurgents, and in some case multiple suicide car bombs, as examples of the new tactics.

The first was what military officials described as a well-coordinated ambush south of Baghdad on March 20 on a US military convoy by some 40 to 50 insurgents firing rocket propelled grenades and small arms. Seven US soldiers were wounded. US officials said 26 rebels were killed.

On April 2, the Abu Ghraib prison was assaulted at night by 50-60 guerrillas. The attack opened with a car bomb on one side of the prison, followed by mortar, rocket propelled grenade and small arms fire, and punctuated by a second car bomb on the other side of the prison.

Officials said 44 US soldiers and 12 prisoners were wounded.

On April 11, 40-50 insurgents struck a US military outpost in the western city of al-Qaim near the Syrian border, detonating three suicide car bombs. Three marines were reported wounded and the insurgents nearly breached the compound with a car bomb.

A Pentagon official noted that two attacks over the weekend each featured double car bombings.

US commanders have played down the attacks as "desperate acts by desperate individuals."

Pentagon spokesman Lawrence DiRita said last week that commanders wondered whether insurgents were marshalling their "dwindling capacity" to carry out fewer but better coordinated and more spectacular attacks.

But a violent new phase of the insurgency could set back US hopes for making significant reductions in its 142,000-strong force next year.

"There is a heightened level of interest because this clearly discernable down trend (in attacks) has changed in the last couple of weeks," the Pentagon official said.

"Does it indicate more planning, more coordination, more sophistication on the part of insurgents? Or is it attributable to some other factor?" he said.

The official suggested that one factor could be a slackening by the Iraqi security forces as they await the new government.

US Defense Secretary Donald Rumsfeld warned Iraq's new Shiite leaders during a visit to Baghdad earlier this month against purging the country's security forces.

Deputy Defense Secretary Paul Wolfowitz followed up with phone calls to Iraqi leaders last week as part of a coordinated effort by top administration officials to press for the naming of a new government, the senior defense official said.