The United States on Wednesday froze most aid to Niger and imposed travel bans on some officials in response to President Mamadou Tandja's moves to extend his rule over the impoverished West African nation.

"In response to President Tandja's refusal to relinquish his mandate, the United States is suspending its non-humanitarian assistance to the Government of Niger," the U.S. State Department said in a statement.

The United States contributes about $30 million annually to development in Niger, one of the world's poorest countries.

The State Department said the travel bans would cover certain Niger government officials as well as other individuals who support policies that undermine Niger's return to constitutional rule.

The European Union in November froze all development aid for Niger, where Tandja defied international and domestic criticism by holding an August referendum that allowed him to retain power for another three years.

U.S. President Barack Obama, who this month called for more democracy in Niger, on Wednesday ordered it removed from the list of African states enjoying trade benefits under the African Growth and Opportunity Act (AGOA).

Guinea and Madagascar, which also have seen coups in recent months, also were removed from the U.S. list.

Last week the U.S. Millennium Challenge Corporation froze $20 million in aid to Niger to protest Tandja's drive to extend his powers in the country, a uranium producer.

Tandja's move was one of a string of disputed elections and controversial steps by incumbent leaders in West Africa this year to consolidate power, prompting concerns that fragile democratic advances in the region have been undermined.

Tandja argued that he needed to extend his rule to oversee projects such as French energy firm Areva's Imouraren uranium mine, a Chinese-funded oil project and a hydroelectric dam. His original term was due to end on December 22 but he has shown no sign that he is prepared to stand down.