In a live Q&A with VOA News Now, Alisha Ryu gave an update on a car bomb at a checkpoint manned by U.S. forces in central Iraq, near the town of Najaf. She spoke with Doreen McCallister.

McCALLISTER: A car bomb explosion at a checkpoint manned by U.S. forces in central Iraq apparently has killed four American soldiers. VOA's Alisha Ryu is traveling with the 3rd U.S. Army Infantry Division in Central Iraq. Alisha, what is the latest?

RYU: Well, more information has been coming about this incident. I had reported earlier that there was a civilian vehicle. We believe now that it was a civilian taxi, and it was not a collision - ramming situation - that we had initially thought. It was actually a man sitting inside a taxi. He was pretending that his car had broken down. Several soldiers went over to investigate, and that's when the bomb detonated. So, it was actually a suicide bomber that was sitting inside the car. That is according to the U.S. Army here. That is still an initial report. That has not been confirmed. There are people on the ground trying to assess what had happened, and how many have really, actually been killed. Of course, the man sitting inside the car is dead as well.

There is no indication really of who carried this act out. However, suspicion is falling on a member of the al-Quds unit. Al-Quds is a martyr-for-Saddam-type of unit that has been recruited by the Saddam Hussein government to fight for the regime. That has not been confirmed, but that is where the suspicion lies at the moment.

McCALLISTER: Was this the first time there was a bombing at the checkpoint?

RYU: This is the first time that there has been a car bombing, and a suicide car bombing at that. Previous incidents have all been very limited to pickup trucks that have been harassing U.S. soldiers - gun-mounted pickup trucks; those kinds of situations with small arms fire. This is the first time that they have actually resorted to suicide attacks. And, I can tell you that security has been massively heightened all over Iraq. There have been - they are taking this very, very seriously. And, they will make sure that security at those checkpoints is increased, and everybody remains vigilant from now on.

McCALLISTER: Before today's suicide bombing, what was the mood like of the troops that you're traveling with?

RYU: The troops are holding up quite well, given the difficult circumstances. Of course, the use of civilian disguises by the [Iraqi] troops - these paramilitary units, such as the fedayeen, the al-Quds and other paramilitary elements that have been sent down here - that includes the special Republican Guards elements, that have been sent down from Baghdad, the personal bodyguards of Saddam Hussein, they have been very, very ruthless and very terrorist-like in their attempts to try to harass and try to slow the advance of the U.S. force. This has been very worrisome to the troops, certainly. But it has not been much of a concern in the sense of overall objectives, or the war plan. And, I don't think that has changed. It has just increased concern about the safety of the soldiers here. And that will remain heightened, I believe, for the foreseeable future.