Thai security forces have arrested four suspects and stepped up investigations after a wave of bombings in southern Thailand left one person dead and injured more than two dozen. The attacks led to a call by the Thai army chief for the government to consider talks with insurgent leaders.

The arrests Friday came as the Thai military and police intensified the search for other Muslim insurgents suspected in the bombing attacks a day earlier.

Thai police officers examine the damage inside the Yala branch of Kasikorn Bank after a bomb exploded Thursday, Aug. 31, 2006 in Yala province, southern Thailand

The wave of bombings struck 22 bank branches in southern Thailand's Yala province, killing one man and injuring 27 people. The blasts, which occurred within a few minutes of each other, were triggered by mobile phones.

Thai police say closed-circuit TV showed explosives being placed in trash cans, newspaper stands and close to seats held by women and teenagers dressed in school uniforms. The explosions were detonated as the banks were crowded with customers depositing their monthly pay.

Sunai Pasuk, a Thailand representative of the U.S. group Human Rights Watch, says the attacks show the insurgents are focusing on new targets.

"Previously, they attacked symbols of the state such as government locations, army barracks, security checkpoints or schools - but never before would they single out commercial banks," said Sunai. "So this means nothing is spared in the south."

For the past two years, three provinces bordering Malaysia have been hit by nearly daily attacks from Islamic militant groups. The attacks have mostly been aimed at schools, government workers, Buddhist monks, and Muslims who are viewed as collaborating with the government.

The three southern provinces are home to most of Thailand's four million Muslims, many of whom complain of discrimination in the predominantly Buddhist country.

The head of the Thai Army, General Sonthi Boonyaratklin, has called for talks with the insurgents to end the violence. The government has so far refused to hold talks, saying it will not negotiate with terrorist organizations.

Human Rights Watch's Sunai says the latest attacks highlight the gains the insurgents have made since the violence began in January 2004. More than 1,500 people have died since then.

"The insurgents have proved that they are making significant headway in establishing control into the urban community," added Sunai. "After the attack they simply disappeared, which means they have moved in so close right under the nose of the Thai authorities."

Thai intelligence sources say the groups' demands include greater political, economic and social rights in the southern provinces.

Some reports have said the insurgents seek to break the south away from Thailand, although security officials doubt the insurgents would seek full independence.