BEIRUT - Lebanese Prime Minister Fuad Siniora has decided to attend the Arab summit in Khartoum, an aide said on Monday, in a challenge to pro-Syrian President Emile Lahoud whose mandate the minister's allies deem unconstitutional.

Lahoud was already scheduled to attend the summit starting Tuesday but a government source said the head of state's participation was not sufficient to represent Lebanon.

"This decision (for Siniora to go) is aimed at making up for the inadequate representation of Lebanon which is limited to the president of the republic," said the source, who asked not to be named.

The anti-Syrian majority in Lebanon's parliament have contested Lahoud's right to represent his country at the summit, arguing that he is only still in office as his mandate was extended by Syria.

In September 2004, the previous Lebanese parliament extended Lahoud's mandate by three years in the face of opposition from a majority of Lebanese and a UN Security Council resolution.

Lebanon's political landscape was transformed last year by the withdrawal of Syrian troops, after a three decade presence.

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