Thailand's foreign minister has resigned amid a political row over an ancient temple on the Thai-Cambodian border.

Noppadon Pattama, who was targeted for impeachment by the opposition Democrat Party, told reporters his resignation would take effect on Monday.

"I want to see national reconciliation. In order for the government to continue working to solve the country's problems, I resign," he said in remarks broadcast on national television.

He is the second cabinet member to resign in two days, increasing pressure on the government of Samak Sundaravej, the Thai prime minister, who was installed just five months ago.

Democratic Party politicians had accused Noppadon of supporting Cambodia in a row over the cliff top Preah Vihear temple that both countries claim as their own.

On the same day however Thailand's constitutional court ruled that Noppadon acted unconstitutionally when he endorsed Cambodia's Unesco application without first consulting the Thai parliament on the matter.

Announcing his resignation on Thursday an emotional Noppadon said he was quitting to "take responsibility so that the country can move forward".

"I insist that I have done nothing wrong. I have not sold out the country. I love Thailand, and would not cause any damage to the country."

Ctitics said the endorsement undermined Thailand's own claim to land near the temple.