Four Thai soldiers have been wounded in a bomb attack in southern Thailand, less than a day after three other blasts killed two and injured dozens. The Thai government is considering stepping up security in the mainly Muslim south.

The bomb that injured four soldiers Monday in southern Yala Province exploded as Thailand was counting the cost of bombings at a provincial airport and two foreign-owned department stores, which left two people dead and nearly 30 injured.

Thai Prime Minister Thaksin Shinawatra has said he may boost troop numbers in key southern provinces. The move would mark a step back from earlier plans to withdraw troops in a bid to ease tensions between the government and the south's Muslim community.

About 20,000 troops are stationed in the three southern provinces of Narathiwat, Yala, and Pattani.

But the latest bombings at the airport and department stores were in the previously more peaceful Songkhla Province.

Chulalongkorn University political scientist Panitan Wattanayakorn says these attacks represent a change in strategy by insurgents, due to the tight security in some southern areas.

"The number of troops have been sending up to, near 20,000, has been reinforced in the area," he said. "The perpetrators cannot use old tactics, so they are now pressed to adopt more new techniques and more flexible approaches."

A week earlier, several members of the security forces were wounded when militants attacked a train.

Thai authorities have blamed Muslim separatist groups for the violence that has led to more than 700 deaths in the past 15 months.

Human-rights groups, often vocal critics of Prime Minister Thaksin's previous hard-line security stance, condemned the bombings.

But in calling for those responsible to be brought to justice, rights group Forum Asia cautioned authorities against using "extra-judicial means," such as arbitrary arrest and detention.

Australian Defense Minister Robert Hill, visiting Thailand as part of a tour of three Southeast Asian nations, discussed the southern situation with Thai Defense Minister Thammarak Issarangkmura na Ayudhaya.

Mr. Hill says, despite increased regional efforts to halt terrorist attacks, challenges remain.

"Whether we are winning overall, I do not think anybody can say at the moment," he said. "The challenge is to just to keep addressing the threat in a most effective way."

The violence in the past year is the most severe since the 1970s and 1980s, when the Thai government used a strategy of amnesties, negotiation, and improved local security to halt a Muslim insurgency.