Clark said things may escalate in the region if the Federal Government stalls further in taking decisive actions on the dialogue process.
Clark gave the warning on Thursday, January 5, at a meeting of Pan Niger Delta Forum (PANDEF) held at his Delta residence.
He said things may get out of hands if the Muhammadu Buhari administration does not take fast and progressive actions on the crisis.
The Ijaw leader, however, commended the President for acknowledging that dialogue is the solution to the incessant attacks on oil facilities in the region.
Clark said: "When Mr. President gave his New Year message, he paid particular attention to peace in the Niger Delta.
"He said he was prepared to dialogue with Niger Delta people. And he used the word, ‘I am persuading’, the second time he was using that word. So we congratulate him for the first time of agreeing that dialogue is the answer.
"So we are ready, but no impression should be given that they are still looking for people to negotiate with, because on the 1st November, last year, we met with him, we were about a hundred; traditional leaders, opinion leaders, youths, women, we all met at Aso Rock.
"We were therefore very happy when he decided that no armed conflict. November to January is a long time. We have been waiting and we were surprised that one of his media aides came to the television to say they are still looking for credible people to negotiate with. That’s a grave insult to us."
He also called on the Federal Government to urgently "arrest the situation" in Southern Kaduna, where over 800 people were reportedly killed by Fulani herdsmen on Christmas day.
"We are interested in everything happening in this country. We are particularly concerned about the killings in Southern Kaduna," he said.
"We condemn what is going on in the area. The federal government should show interest. Nigeria should have peace. Our economy is going down and it’s only in atmosphere of peace our economy can grow.
"We are all Nigerians and we are all equal in this country. Nobody should pick religion or ethnicity in the affairs of this country. The federal government should as a matter of urgency arrest the situation before it turns out a full blown war."
Other elders present at the meeting were said to have risen to the defense of one of their own, former president Goodluck Jonathan, pointing that it appears the Federal Government deliberately plots to humiliate the Jonathan family
They expressed worry over the "seeming silence of President Buhari in the frequent harassment" of members of the ex-president's family by the Economic and Financial Crime Commission (EFCC).
They also demanded the immediate release of the over N1trillion federal government under-contribution to the Niger Delta Development Commission (NDDC) funds.