Mr Tandja's plans have caused outrage in Niger and overseas
Niger's president has said he will not bow to foreign pressure to abandon his attempt to hold a referendum on whether he can serve a third term in office.
Mamadou Tandja told state TV the threat of sanctions would not deter him from doing what was right for the people.
On Tuesday he met Un and African envoys who said they were "deeply concerned" over his attempt to remain in power.
A court has ruled that a general strike called by the opposition is illegal and it is not clear if it will go ahead.
The EU has already suspended some aid to the uranium-rich nation.
The West African regional body, Ecowas, has threatened Niger with sanctions or suspension if Mr Tandja goes ahead with the referendum, scheduled for 4 August.
In a televised address, the president said he did not come to power to "serve international opinion".
"I won't let anyone prevent me from achieving a useful goal for the people of Niger," he said.
In recent weeks Mr Tandja, 71, has dissolved parliament and abolished the Constitutional Court after both institutions opposed his proposed referendum.
The proposals have sparked large-scale protests in the capital, Niamey, and the opposition has accused him of staging a coup.
Mr Tandja was first elected in 1999, and then again five years later.
He had previously promised to quit in December this year, a month after presidential elections are due to be held.
But the president's supporters argue he should be allowed a third term, saying he has reduced poverty in the country in the 10 years he has been in power.