BANGKOK (AFP) - Twenty-six people accused of plotting an attack in Thailand have been indicted by a military court on charges including weapon possession and conspiring to commit terrorism, their lawyer said Saturday.

The suspects were arrested in northeastern Thailand - a traditional stronghold of fugitive premier Thaksin Shinawatra - after the army seized power in a bloodless coup on May 22.

The 24 men and two women - whose ages range from 40 to 72 years old - were indicted by a military court in the northeastern city of Khon Kaen on Friday, their lawyer Winyat Chatmontree told AFP.

He said the group - named the "Khon Kaen Model" by the army - include farmers, a bank security guard, a school director and business owners.

Some of them are followers of the "Red Shirts" protest movement, which broadly supports Thaksin, according to Winyat.

Most of them were seized in an apartment a day after army chief Prayut Chan-O-Cha overthrew an elected government allied to Thaksin.

"The army arrested them and found guns, hand grenades, knives - things you're not allowed to have without permission," said Winyat.

"But they said other people asked them to keep them," he added.

He said the maximum sentence, if convicted, was the death penalty, although executions are now rare.

At the time of their arrest, the army said the suspects were allegedly intent on a "large-scale attack" in Khon Kaen, one of the largest northeastern cities.

The suspects are being held at a civilian prison in Khon Kaen.

Street violence linked to months of mass opposition rallies left nearly 30 people dead before the May coup.

Since seizing power the junta has abrogated the constitution, curtailed civil liberties under martial law and summoned hundreds of opponents, activists and academics for questioning.

Experts say there are armed elements on both sides of Thailand's bitter political divide.

Thaksin, who was ousted in an earlier coup in 2006, has traditionally enjoyed strong support in the northern half of Thailand thanks to populist policies such as nearly-free healthcare, micro-loans and generous rice farming subsidies.

He fled Thailand in 2008 to avoid jail for a corruption conviction.

Thaksin or his allies have won every election since 2001, most recently in 2011 under his younger sister Yingluck Shinawatra, who was removed from office in a controversial court ruling shortly before the latest coup.

The army says its power grab was necessary to prevent further violence but opponents see it as an attempt to suppress Thaksin's political dominance.

The junta has ruled out holding elections before around October 2015.