ACCRA - Ghana's presidential election headed for a second round run-off, electoral and party officials said on Tuesday, as the frontrunners seemed unlikely to secure an outright victory.

Although provisional results from Sunday's elections in the West African state showed the candidate of Ghana's ruling New Patriotic Party (NPP), Nana Akufo-Addo, with an early lead, as more votes came in the run-off scenario gathered strength.

The electoral commission will announce full results on Wednesday and confirm the likely need for a run-off between Akufo-Addo and his nearest rival. It would be held on Dec. 28.

The Ghanaian polls are viewed as a test for African democracy after flawed elections elsewhere on the continent.

Analysts say the contest is especially keen as the gold- and cocoa-exporting nation, seen by investors as one of Africa's most promising emerging markets, looks forward to greater prosperity when offshore oil comes onstream in late 2010.

With votes counted from 175 of the 230 constituencies, the electoral commission had announced that Akufo-Addo had 50 percent, against 46 percent for National Democratic Congress (NDC) opposition leader John Atta Mills.

But a senior commission member, who asked not to be named, said it appeared neither of the two leading contenders would finally obtain the minimum 50 percent plus one vote required to win the election outright in the first round.

"It's headed for a run-off ... it is likely," he said.

Party officials monitoring vote counting at the electoral commission also confirmed this likelihood.

"We have been called this evening by the electoral commissioner who told us that results so far collected indicated that there may not be a clear winner in this first round," Victor Smith, an NDC official at the commission, said.

"We are aware there is going to be a run-off and we are prepared for it," NPP General-Secretary Nana Ohene Ntow said.

Foreign observers were full of praise for the elections to choose a new parliament and a successor to President John Kufuor, who steps down in January after the maximum two terms.

Besides Akufo-Addo and Mills, six other candidates stood.

Mills' NDC had said on Monday its candidate had won in the first round and denounced what it called an attempt to rob it of victory. The ruling NPP denied trying to cheat and said it, rather than the NDC, would win.

The vote for the 230-seat parliament was earlier reported to be neck and neck. Of seats already decided, the NPP had 78 and the NDC 77, indicating the NPP may lose its domination of the National Assembly. It had 128 seats in the outgoing parliament.

Foreign election observers reported some procedural and organisational problems in Sunday's polls but generally praised them as reinforcing Ghana's commitment to democracy.

"Polling was conducted in a calm and generally orderly manner...EU observers assessed the overall environment positively," the European Union observer mission said.

Monitors from the U.S.-based Carter Center, founded by former U.S. President Jimmy Carter, also commended the vote.

"Ghana is becoming a model of democracy in the region and abroad," former Botswana President Ketumile Masire said, reading a statement from the Carter Center observer mission.

There was isolated violence.

Around 400 supporters of one parliamentary candidate attacked electoral officers and their escort, seizing two ballot boxes from a polling station in Dambai, in the mainly pro-NDC Volta Region, regional police chief Bernard Dery told Reuters.

Ghana's fifth set of elections since embracing multiparty democracy in 1992 has drawn attention as a chance to prove an African state can hold credible ballots, after election-related violence this year in Kenya, Zimbabwe and Nigeria.

"The December 7, 2008 elections in Ghana have the potential to redeem the image of democracy and the rule of law in the continent," an electoral observer mission from the Economic Community of West African States said.