Soldiers in Niger say they have removed President Mohamed Bazoum from power, after armed troops earlier blockaded the presidential palace in Niamey, the capital in one of the world’s most unstable nations.

A group of soldiers appeared on the west African country’s national television late on Wednesday, a few hours after the president had been detained.

Reading from a statement, Colonel Amadou Abdramane, seated and flanked by nine other officers wearing fatigues, said the defence and security forces had decided to “put an end to the regime that you know due to the deteriorating security situation and bad governance”.

He said the country’s borders were closed and all institutions of the republic suspended, and announced a national curfew. The soldiers warned against any foreign intervention.

The apparent coup was said to be led by the head of a regional political and security group.

The soldiers, including members of the presidential guard of Bazoum, were earlier said to be engaged in negotiations with the president – who was described as “safe and well” although his location was unclear.

The move by the elite guard force was quickly challenged by the wider army and national guard, who threatened to attack the presidential force unless they stepped down.

The White House said as the situation unfolded that the US secretary of state, Antony Blinken, had spoken to the captive Bazoum and “conveyed the unwavering support of the United States … the strong US economic and security partnership with Niger depends on the continuation of democratic governance and respect for the rule of law and human rights”.

Blinken, visiting New Zealand, later said: “I spoke with President Bazoum earlier this morning, and made clear that the US resolutely supports him as the democratically elected president of Niger. We call for his immediate release.

“We condemn any efforts to seize power by force. We’re actively engaged with the Niger government, but also with partners in the region and around the world, and will continue to do so until the situation is resolved appropriately and peacefully.”

The UN said its secretary general, António Guterres, also spoke to Bazoum and offered his “full support and solidarity”. Guterres called “on all actors involved to exercise restraint and to ensure the protection of constitutional order”.

A source close to Bazoum described the move as a “fit of temper” by the elite troops adding that “talks” were under way after the soldiers blocked access to the palace at about 6.30am on Wednesday.

A Reuters reporter saw military vehicles blocking the entrance to the palace in the capital, Niamey. Access to ministries next to the palace had also been blocked, security sources said. Residents in other parts of the city described traffic moving freely and no evidence of armed men on the streets.

An official in the presidency said staff inside the palace did not have access to their offices, while a statement issued by the presidency on Twitter suggested that the presidential guard had tried to win over the support of some members of the armed forces in their actions.

The chair of the African Union Commission, H E Moussa Faki Mahamat, condemned what he called an “attempted coup”. If confirmed, it would be the fifth attempted coup in west Africa in the past four years.

The country is struggling with two jihadist campaigns – one in the south-west, which swept in from neighbouring Mali in 2015, and the other in the south-east, involving jihadists based in north-eastern Nigeria.

Niger’s military has received training and logistical support from the US and France, which have military bases there.

“It’s a fit of temper by the presidential guard but talks are under way with the president,” the source told the AFP news agency, speaking on condition of anonymity.

“The president is fine, he’s safe and sound,” the source said. “He and his family are at the residence.”

The reason for the guards’ behaviour and what was being discussed in the talks were not given.

An MP with Bazoum’s PNDS party said: “I spoke to the president and to friends who are ministers [and] they are fine.”