At a press conference at his headquarters in Baghdad, Adnan al-Dulaimi, a notable Iraqi figure, condemned foreign parties who "want to change Iraq's Arab-Muslim identity".
"Sunni Arabs are responsible for this country's history, unity and identity," he said.
He said Sunni religious leaders would urge Arab Sunni Muslims to participate in the coming elections later this year.
Meanwhile, new Sunni delegates are expected to meet later on Tuesday with the parliamentary committee that is drafting a new constitution.
Washington and Baghdad are trying to use diplomacy and politics to defuse an uprising that has grown much more violent since the government took power in April after a January election in which few Sunnis took part.
Iraq's parliament formally welcomed on Tuesday 15 new Sunni Arab members to the committee tasked with writing a constitution, making it the first national political body to include significant representation from Saddam Hussein's formerly dominant minority since the election.
The committee was expanded to
include extra Sunni Arabs
The committee was expanded to 71 members to include more Sunni Arabs. Previously there were just two.
The committee, which must agree on a draft constitution by 15 August ahead of an October referendum and December election, will have its first full meeting on Wednesday, committee chairman Humam Hamoudi said.
He said the main points of contention would probably be the extent to which the constitution described Iraq as an Arab state, and the boundaries and degree of autonomy of federal regions, such as the mainly Kurdish north.
Western diplomats observing the process have said arguments over the structure of government - expected to be broadly a parliamentary rather than presidential system - may be extensive, as may any clause on the rights of women.
"The really hard bargaining hasn't started yet," one Western diplomat said last week. "It'll get into the really heavy-duty horse-trading at the end of the month."