Lebanon will boycott the Francophone summit, scheduled to be held in the Romanian capital of Bucharest in September, if its president is not invited, the president's office said on Wednesday.
"It is really astonishing for the French state to adopt this position," the president's office said in a statement late on Tuesday. "It regrettably confirms the information about direct interference by French President Jacques Chirac."
Lahoud has been boycotted by France as well as the US since his term in office was controversially extended for three years in September 2004 under pressure from powerful neighbour Syria.
Jean-Baptiste Mattei, the French foreign ministry spokesman, said on Tuesday that Lahoud had not been invited by Romania to a Francophone summit in October and that Lebanon would be instead represented by Fuad Siniora, the prime minister.
Lahoud's office said: "This is a direct interference in Lebanese internal affairs and is a flagrant violation of the constitution which stipulates that the Lebanese state, through its institutions, decides the level of its representation, and not any other state, including the host country."
Lahoud's office, which did not however criticise Romania for failing to invite him, noted that the president had chaired Lebanese delegations to several international summits and to the last UN General Assembly in September.
Mattei said the decision not to invite Lahoud was because the extension of his term violated terms of UN Security Council Resolution 1559 sponsored by France and the US which had called for free and constitutional presidential elections in Lebanon.
Lahoud's term was extended for three years in 2004 under a constitutional ammendment backed by Syria, which had been the main power broker in Lebanon until domestic and international protests forced it to end its 29-year military presence.
Earlier this year, Lahoud's office accused Chirac of personally working towards ousting the Lebanese president - a claim denied by France.