AUSTIN (Texas) • A man who terrified Texas residents with a three-week bombing campaign that killed two people blew himself up on the side of a highway north of the city of Austin as police closed in on him early yesterday, said police officials.

An official identified the suspect as Mark Anthony Conditt, an unemployed 24-year-old.

Police had tracked the suspect to a hotel near Austin, the state's capital city, and were following his vehicle when he pulled to the side of the road and detonated a device, killing himself.

"The suspect is deceased and has significant injuries from a blast that occurred from detonating a bomb inside his vehicle," Austin police chief Brian Manley told reporters. He said the suspect was white.

The police chief said that the suspect was believed to be responsible for six bombs around Austin, including five that detonated, since March 2. He said it was not yet known what motivated the bombing campaign or whether the suspect had help.

He also warned that it was not clear whether any more bombs had been left in places around the city.

The series of bombings killed two people and injured at least five others, unnerving residents of Austin, which has some one million people.

The first three devices were parcel bombs dropped off in front of homes around Austin neighbourhoods. A fourth went off on Sunday night, apparently detonated with a trip wire, and one exploded inside a FedEx sorting facility on Tuesday.

The series of bombings had bewildered law enforcement officials, who by Sunday began taking the unusual step of publicly calling on the bomber to get in touch and explain why he was carrying out the attacks.

The first two bombs killed black men, raising fears that they were part of a hate crime, but investigators said the later, more random blasts made that less likely.

Police found the suspect at a hotel in Round Rock, Texas, about 32km north of Austin. While officers were waiting for reinforcements, the suspect drove away.

He later pulled off the city's main highway and set off his device as two police officers were approaching his vehicle. One officer was injured in the blast.

Officials warned residents not to let their guard down yet. "We still need people to be vigilant," said Austin Mayor Steve Adler. "We don't know where the suspect has been the last 24 hours."

REUTERS, AGENCE FRANCE-PRESSE, NYTIMES