Burundi's new president has warned opposition parties that they "would no longer get space" in the country, questioning "why should one oppose the government".
Evariste Ndayishimiye made the statement during his hour-long inauguration speech on Thursday.
He also promised freedom of expression and protection of human rights.
The fast-tracked inauguration ceremony came after his predecessor Pierre Nkurunziza died suddenly last week.
Mr Ndayishimiye had been due to take power in August after being declared the winner of May's presidential election, in which he was the candidate of the ruling party. The opposition said the poll was rigged.
No foreign heads of state were present when he took the oath of office in the administrative capital, Gitega, where he pledged to defend the nation's interests and unify its citizens.
In his speech, the new president also asked media and human rights activists to partner with the government to tackle national issues, otherwise "they will be work for others, not Burundians".
He also called for Burundi's refugees to return home but warned them not to destabilise the country.
People attending the inauguration were told to arrive early to allow time for temperature checks and other coronavirus measures - but once in the stadium there was no social distancing.
Mr Nkurunziza died aged 55 on 8 June after suffering a cardiac arrest, the government said. There are unconfirmed reports that he was suffering from Covid-19.
He had been in power for 15 years.
According to Burundi's constitution, if the head of state dies in office then the president of the national assembly, currently Pascal Nyabenda, should succeed him.
But after a ruling by Burundi's Constitutional Court, Mr Ndayishimiye's inauguration in Gitega was brought forward.
Who is Evariste Ndayishimiye?
By Cyuzuzo Samba, BBC Great Lakes
The 52-year-old army general is regarded as a "humble" and "religious" man.
He has been among the most influential generals since 2005, when his close friend and colleague in rebellion, Pierre Nkurunziza took power.
Mr Ndayishimiye, commonly known as "Neva", was a law student in the University of Burundi when the civil war erupted in 1993 following the assassination of President Melchior Ndadaye.
Like his predecessor Mr Nkurunziza, in 1995, Mr Ndayishimiye survived an attack on ethnic Hutu students at his campus in the then-capital Bujumbura. He then fled the country and joined the rebel force that was formed to fight the then Tutsi-led government.
Mr Ndayishimiye worked closely with Mr Nkurunziza during the Arusha peace talks between the government and the FDD rebels.
Following the 2003 peace accord that saw FDD rebels share the power with the government, Mr Ndayishimiye deputised for the then army chief of Burundi. In 2006 he was named minister of the interior, before becoming the president's military adviser and then secretary-general of the ruling CNDD-FDD party.
Mr Ndayishimiye, a father of six, is known as a practising Roman Catholic, and like his predecessor emphasises the role of God in politics. The new president is taking over a country that is diplomatically isolated and on bad terms with donors.
In 2015, the constitution was changed, allowing Mr Nkurunziza to seek a third term, triggering huge protests, an attempted coup and a widespread crackdown.
Thousands of Burundians have fled the country and into refugee camps in neighbouring countries.