A Thai activist opposed to the military's role in politics says he was assaulted by a group of unknown men, in the latest in a series of such attacks.

Sirawith Seritiwat says five or six men attacked him by surprise Sunday night after he had been working on a campaign to petition members of the Senate not to vote this week to appoint current Prime Minister Prayuth Chan-ocha to the post again. Prayuth seized power in 2014 after leading a military coup against an elected government.

Sirawith, also known as Ja New, was hospitalized overnight but his injuries did not appear to be serious. Two other activists who are also critics of the military were attacked in May. No suspects have been identified in any of the cases.