BANGKOK (Reuters) - A junior minister in Thai Prime Minister Abhisit Vejjajiva's month-old cabinet resigned on Tuesday amid a corruption scandal involving rotten canned fish given to flood victims.

Witoon Nambutr, Minister of Social Development and Human Security and a senior member of Abhisit's Democrat Party, denied involvement in the affair, which has rocked the coalition government only a month after it started work.

Witoon, the first Abhisit cabinet member to step down, said he did not know how the bad cans of fish, which made dozens of rural people violently ill, had made it into packages handed out to flood victims by his ministry in the south.

"My resignation is a painful decision as I have not in any way been involved in this. My action is not made under pressure from party members or party executives," he told a news conference.

Another cabinet member, Deputy Interior Minister Boonjong Wongtrairat from one of Abhisit's coalition partners, is also under pressure amid accusations he handed out government cash along with his namecard to villagers last week.

The opposition charged that Boonjong's action was tantamount to vote buying and as such breached the constitution. He has denied the charge.

The Oxford-educated Abhisit has a moderate majority, but is under pressure from the rapidly slowing economy and opponents in parliament and on the streets who accuse him of being a puppet of the generals who ousted Thaksin Shinawatra in a 2006 coup.