Yeddyurappa would take the oath alone as the chief minister and once the majority is proved on the floor of the assembly, cabinet members would be inducted, the BJP said.
Governor Vajubhai Vala on Wednesday invited Bharatiya Janata Party legislature party leader B S Yeddyurappa to form the government in Karnataka, capping a day of intense jockeying for power and allegations by the Congress of bribery and horsetrading against the BJP and Prime Minister Narendra Modi.
'I invite you (Yeddyurappa) to form the government and be sworn-in as the Chief Minister of Karnataka,' a Raj Bhavan communique said.
Vala also asked 75-year-old Yeddyurappa to seek a vote of confidence within 15 days of assuming office as the chief minister.
Briefing reporters, BJP General Secretary Muralidhar Rao said Yeddyurappa will take oath here on Thursday at 9 am.
Prime Minister Modi and BJP chief Amit Shah are unlikely to attend the swearing in ceremony, party sources said.
Toiling hard to control the levers of power in Karnataka, Yeddyurappa and H D Kumaraswamy, the leader of the newly formed Janata Dal-Secular-Congress alliance had earlier met Vala and staked claim to form the government.
The BJP asserted it would prove its majority in the assembly and dubbed the Congress-JD-S post-election alliance 'unholy and unacceptable'.
Rao said the understanding between the Congress and JD-S was only 'to keep the BJP off'.
"It is a complete subversion of the mandate and democratic process and it should be treated as sabotage of the people's expression which is sacred in democratic process," he told reporters in Bengaluru.
"People of Karnataka know this is an unholy and unacceptable alliance," Rao said.
On the governor's invitation, he said, "We had submitted our willingness and claim... being the single largest party we are accepting the responsibility and expressing the willingness to form the government."
He said BJP had always followed the core democratic principles that when there was no clear mandate.
"In such a situation when there is no pre-poll alliance, the single largest party should be given an opportunity to form government and prove majority on the floor of the house.
"We will prove the majority on floor of the house which is part of directive from the Governor," he said.
Rao said Yeddyurappa would take the oath alone as the chief minister and once the majority is proved on the floor of the assembly, cabinet members would be inducted and expansion would take place.
With 104 MLAs in the 224-member assembly, the BJP is the single largest party, while the JD-S-Congress coalition, formed after the election results were declared, has 116 legislators. It has also claimed support of an independent MLA.
With there being precedents of both governors inviting either the leader of the single largest party or that of a post-poll coalition to form the government, Vala, a former Rashtriya Swayamsevak Sangh-BJP veteran from Gujarat, opted for the former.
The BJP said the Governor has acted as per Constitution and the Supreme Court's orders by inviting Yeddyurappa and accused the Congress of trying to 'loot' the mandate.
At a press conference, Union minister Ravi Shankar Prasad accused the Congress of threatening violence in the state if it was not invited by the governor to form government and said it has resorted to 'shameful and irresponsible' tactics.
He also said the opposition party's charge that the BJP was trying to buy out MLAs of other parties should be rejected with the 'contempt it deserves'.
Asked about the Congress' claim that the governor should have followed the precedent of Goa and Manipur, where the Congress emerged as the single largest party but the BJP and its post-polls allies were invited to form government, he said the opposition party never staked a claim for forming government in those two states.
Prasad also cited the reports of the Sarkaria and Punchhi commissions, both on the Centre-state relations, and said they had recommended that a governor in the case of hung assembly verdict should first invite the largest pre-poll alliance followed by the largest single party and then the post-poll alliance in that order of preference.
A Constitution bench of the Supreme Court 'endorsed' this as well, he said, suggesting that the Karnataka governor's decision was in line with the two reports.
The apex court has also agreed with the discretionary powers given to the President and the governors by the Constitution, and stated that it should not be arbitrary, Prasad said.
The senior BJP leader cited the then outgoing prime minister Rajiv Gandhi's decision in 1989 to not stake claim to form the government at the Centre despite the Congress emerging as the single largest party saying the mandate was against his party.
"I want to ask Congress president Rahul Gandhi and his mother Sonia Gandhi when their party is preaching us about the Constitution and democratic norms that if they have forgotten the legacy of their own family," Prasad said.
Asserting that people's verdict in Karnataka was against the incumbent Congress, he said its tally was reduced was to 78 from 122 with Chief Minister Siddaramaiah losing from one constituency and 16 ministers facing defeat as well.
The Congress is unable to resist the temptation of grabbing power in the state and is riding "piggyback" on the JD(S), against which it fought the poll bitterly, Prasad said.
"The Congress is trying to loot the mandate," he alleged.
Prasad said the Congress should not 'preach' as it has a history of making a mockery of the Constitution.
The Congress imposed the President's rule in states with democratically-elected governments and its prime minister once faced a trial over his attempts to turn his minority government into a majority dispensation, Prasad alleged, apparently referring to P V Narasimha Rao.
Slamming Vala's invite to Yeddyurappa, Kumaraswamy accused the Modi government of misusing Constitutional institutions.
"We will not let it go easily...," a furious Kumaraswamy told reporters in Bengaluru shortly after the governor wrote to Yeddyurappa.
Kumaraswamy said the governor should have given three or four days time for Yeddyurappa to prove his majority. "He (Yeddyurappa) has no majority," Kumaraswamy said.
Earlier in the day, Kumaraswamy claimed the BJP had offered his MLAs Rs 100 crore and ministerial berths to break ranks and back the saffron party.
The allegations were promptly dismissed by the BJP, with Union minister Prakash Javadekar dubbing them as 'imaginary'.
Outgoing chief minister Siddaramaiah also alleged the prime minister was encouraging 'horsetrading' to ensure the BJP returns to power in the state despite falling short of a majority.
"Our MLAs were offered Rs 100 crore by the BJP to break away. I want to know whether this is black or white money," Kumaraswamy told a press conference.
The Congress lambasted Vala for inviting the BJP, accusing him of acting like a 'BJP puppet' and allowing the saffron party to 'manufacture' a majority in 15 days.
Congress leader P Chidambaram also alleged that the Governor has given Yeddyurappa 15 days time to "convert" the number of 104 legislators to 111.
'Governor invites Mr Yeddyurappa to manufacture a majority in 15 days. Governor gives Mr Yeddyurappa 15 days to convert the number 104 into 111,' he tweeted.
Party general secretary Ashok Gehlot said that the decision was a 'murder of democracy' and has been taken 'under pressure from the BJP leadership'.
"It is a murder of democracy in the country and it is a black day in India's history...The decision has been taken under pressure of BJP leaders," Gehlot told PTI.
Gehlot expressed concerns over the development and said people of the country are "worried" over the direction in which the country was moving.
Congress' chief spokesperson Randeep Singh Surjewala also hit out at Vala, accusing him of denigrating the Governor's office, trampling upon Constitution and abusing law and acting like a 'BJP puppet'.
Vala, Surjewala charged, chose to serve "his masters in the BJP" than serving the Constitution.
'Vajubhai Vala denigrates the Governor's office,tramples upon Constitution,abuses the law & acts as a BJP puppet. He chooses to serve his Master's in BJP rather then serve the Constitution. As @BJPKarnataka informed in advance, orders come from BJP HQ then the sanctity of office," he said on Twitter.