Thammasat University historian Somsak Jiamteerasakul said yesterday he's ready to fight any lese-majeste charges and prove his innocence - but the military must cease what he called harassment that was frightening his family.

Somsak alleged the military was behind a recent spate of threatening phone calls and motorcycle visits to his home.

"I thought Thailand was more civilised than this. Perhaps I was too optimistic," said Somsak during a press conference at Thammasat University.

The historian, who enjoys a large following amongst critics of the monarchy and often gives public speeches critical of the institution, claimed two "threatening" motorcyclists were sent to his home recently and one was identified as a soldier.

Somsak claimed a high-ranking figure in the government told him the Army wanted the government to "handle" him.

One source, whom Somsak admits can't be identified or proven, told him that 80 soldiers have been assigned to keep an eye on him round the clock, prepared to "pick him up within five minutes' notice".

He warned the authorities that critical voices could not be silenced through censorship and lese-majeste law, adding that the clampdown on freedom of expression would eventually lead to clashes and violence.

Some 500 participants, half of them red shirts, attended the press conference but few mainstream Thai journalists were present.