The Nigerian election commission has suspended the registration of voters in areas of four states which have experienced ethnic and religious violence.

The commission said the process was being halted for an indefinite period in parts of Bauchi, Nassarawa, Plateau and Benue states in Nigeria's "middle belt", according to the BBC's Sola Odunfa in Lagos.

The suspension comes on top of the accusations from opposition parties that widespread inefficiency and fraud are putting Nigeria's voter registration at risk.

The Alliance for Democracy reported "irregularities which can mar the entire exercise and defeat its very purpose", according to the Associated Press news agency.

Among the reported problems were the moving of registration stations without notice, a lack of registration forms and the registration of "ghost voters", who were either under-age or had already been registered.

Sola Odunfa reports that the shortage of registration forms is a major problem and the commission's promise to release more of them has led to accusations that the electoral commission is "hoarding" the materials.

Tempers are rising as the end of the voter registration period approaches.

Sola Odunfa, BBC Lagos

The massive task of registering voters in preparation for state and national elections began on 12 September and will continue for 10 days.

The electoral commission has the task of registering 60 million voters.

Missing forms

Registration cards are not needed for voting alone, they will also be proof of identification for provision of social services and in some business transactions, the BBC's correspondent says.

In some areas of the country, there has been praise for the commission's work - the Governor of Borno State describing registration as a huge success.

Nigeria's electoral roll is years out of date

The suspension in the areas of the Nigerian middle belt has been justified by reference to the recent history of ethnic and religious violence among the different communities there.

The commission does not want to risk further violence.

But there were complaints from the start from the northern Nigerian state of Nassarawa that no registration was taking place in some areas - that was before registration was suspended in other areas of the state.

The Governor of Katsina State also criticised the process, saying that too few forms had been supplied.

But even more serious complaints have been made.

Child voter

"Corruption is fast creeping into the whole exercise," according to the human rights lawyer, Gani Fawehinmi.

"We are collecting reports all over. Multiple registration is not being properly prevented.

"They don't ask for identification, anybody can say they are anyone," Mr Fawehinmi said.

Katsina State Governor Umaru Musa Yar'Adua told journalists at government house on Monday that the whole exercise could be a failure if the commission did not supply enough registration materials.

He said up to 40% of the state's voters would be left unregistered if action was not taken.

The Associated Press reported from a registration centre in Abeokuta, south-western Nigeria, that officials there had registered a male named Dele Ogulowo, who looked no more than 10 years old.

He was registered less than an hour after President Olusegun Obasanjo had visited the centre to check on the registration.

Buying registration cards

AP also cited a businessman in Kano, northern Nigeria, as saying that newly-registered voters could be seen wiping the indelible ink from their thumbs after registering.

The ink is there to prevent people registering more than once.

The businessman, Amadi Chike, added that he had seen people buying registration cards from voters for 150 naira ($1.15).

Obasanjo is facing possible impeachment

But election observers, cited by news agencies, have said that a "few lapses" would not affect the overall registration process.

Presidential elections must come before the current term of President Olusegun Obasanjo - now threatened with impeachment - ends in May.

The electoral commission has called on all voters to register and to see it as the first part of the elections.