He thanked the prime minister for campaigning in the state.
"We are confident of forming the government. We are requesting the prime minister to attend the swearing-in ceremony. It is likely to be held on March 7 or 8," Rio told reporters.
He said discussions are being held to hold the swearing-in ceremony in the open at the Local Ground here.
Rio, a three-time chief minister and a senior leader of the NDPP, an ally of the BJP, staked claim earlier in the day to form a coalition government in Nagaland saying he has the support of 32 MLAs.
More From This Section
The Nationalist Democratic Progressive Party (NDPP) contested 40 seats and secured second position with 18. The ruling Nagaland People's Front (NPF) bagged 27 seats to emerge as the single largest party.
"I am happy but I am not satisfied. It is much below our expectation," the three-time chief minister said while replying to a query by reporters.
Rio said he was grateful to the people of Nagaland and his party colleagues.
Rio said the National People's Party's Nagaland president Ato Yepthomi expressed willingness to extend support to the NDPP-BJP alliance in the formation of the government.
The NPP, an ally of the BJP at the Centre and in Manipur, contested the Nagaland elections for the first time and won two seats.
Yepthomi was seen with NDPP leaders during the day but he refused to comment on this.
On the Supreme Court judgement banning appointment of parliamentary secretaries and advisers, Rio said, "We will go by the rules."
Several Northeastern states had the practice of appointing MLAs as parliamentary secretaries.
To a question, he said he did not think NDPP MLAs could shift their allegiance to any other party.
Asked whether he would accept NPF legislators in the coalition, if approached, said, "I don't see that situation. It is also very good to have a very strong opposition in a healthy democracy.