President Mamadou Tandja changed the constitution to stay in power
Niger's government has expressed its anger over a decision by the regional body Ecowas that it no longer recognises the country's president.
Ecowas said that as it did not condone the referendum that enabled Mamadou Tandja to stay in power, his term had therefore expired on Tuesday.
But the communications minister said no other countries should try to impose their will on the people of Niger.
The West African trade grouping has already suspended Niger.
However, Ecowas said it would continue to mediate in negotiations which began this week between Niger's government and opposition in an attempt to resolve the political deadlock.
'Respect our choice'
"It is a pity that Ecowas took such a stand," Niger's Communications Minister Moctar Kassoum said.
"Niger wants partners that respect our choice; and no country should inflict its ideas on our people who have chosen the voice of the referendum."
The referendum was held in August, after Mr Tandja dissolved parliament as it looked likely to block the vote.
He won a landslide victory. The new constitution allows him to extend his term for three more years without a vote and scraps term limits.
He had been due to stand down on Tuesday after serving two five-year terms.
Opposition groups have described the president's move to stay in power in the uranium-rich nation as a coup.
But his supporters say he should remain as he has brought financial stability to one of the world's poorest nations.
Issaka Souare, a researcher at South Africa's Institute for Security Studies, told the BBC it was the first time an inter-governmental body had not recognised a sitting African head of state.
And he said it would be difficult for Mr Tandja to ignore Ecowas, given landlocked Niger's reliance on its neighbours for trade.
"He cannot afford to be considered as a pariah," he told the BBC's Network Africa programme.
"If you were to compare the situation now in Niger to the one in Zimbabwe, it is different - because while in Zimbabwe the sanctions came from afar, here it is on the doorstep and that is the big difference."