Iraqi insurgent group Army of Ansar al-Sunna said today its fighters were behind the bombing that killed 14 US Marines in western Iraq, according to an Internet statement.
Yesterday's attack was the deadliest against American forces since the start of the war on Iraq.
Ansar al-Sunna has also claimed last year's suicide bombing inside a US military base in which at least 22 people were killed.
"Our heroes planted two high explosive devices yesterday morning once they saw US vehicles moving troops to besiege the town of Haditha," said the statement on an Internet site often used by Iraqi insurgent groups.
"The mujahideen chose the biggest vehicle, the one carrying the most troops, and detonated the devices, causing a massive explosion ... the vehicle was actually carrying 25 Marines and they all died," it added.
Ansar al-Sunna, and the al-Qaeda Organisation in Iraq, have featured prominently in the Iraqi insurgency, launching frequent attacks and killing a number of hostages in Iraq, sometimes by beheading.
Haditha is one of several violent towns in Iraq's western Anbar province, the heartland of Iraq's insurgency which has defied repeated US offensives.