By Haitham Haddadin

KUWAIT, Dec 9 (Reuters) - US State Department official today said that Iran and Syria were trying to destabilise the Western-backed government in Lebanon, where the situation was of ''very significant concern''.

Lebanese opposition parties, spearheaded by pro-Syrian Shi'ite guerrilla group Hezbollah, have protested outside government headquarters in Beirut for the past week to try to topple the cabinet of Prime Minister Fouad Siniora.

''Hezbollah and Iran and Syria are seeking to destabilise the current constitutional government,'' said James Jeffrey, a deputy assistant secretary. ''We think that the situation in Lebanon and several other areas is of very significant concern.'' ''We appeal to the people of Lebanon and the neighbours in the region and the international community to stand up for the principles ... (of) non-interference, non-violence, constitutional processes and rule of law,'' he said.

He said Washington was trying to mobilise moderates in the Middle East and in the international community to support the Lebanese government.

''If any one group, particularly with support from the outside, with the threat of violence, attempts to force its will on the others, we think the situation will get significantly worse,'' he told reporters in Kuwait during a regional tour.

Siniora accused Hezbollah yesterday of plotting a coup against him, a day after Hezbollah chief Sayyed Hassan Nasrallah told thousands of supporters he would not yield in his battle to oust Siniora.

Reuters PDM RS2304