The UN has said that Algeria failed to answer a plea for more security before attacks that killed 17 UN staff in Algiers last month.
The UN has announced an investigation into the bombing
The head of the UN Development Programme, Kemal Dervis, said a "formal request" had received no response.
The UN in Algiers was targeted in one of two suicide bombings claimed by al-Qaeda's North African branch.
The UN has announced an investigation into the attack. Algeria has said the probe is unwelcome.
Mr Dervis said that UN security in Algiers had been at its lowest level last year because previous attacks in the country had targeted the government and "at that time there was no indication that there was any targeting of the UN".
But he said the UN's resident co-ordinator had asked the government "for particular security measures, including blocking off the street, and that the government did not respond to that".
The request had been submitted days after attacks in Algiers last April that killed some 30 people, Mr Dervis said.
Officials had previously said that the UN's former head of security in Algeria, who was killed in the attack, had asked for concrete security barriers outside the offices.
There was no immediate response from Algeria's mission to the UN.
Mr Dervis said that since the 11 December attack Algeria had offered the UN another building, but the UN had rejected it as not sufficiently secure.
"The choice we have at this point is basically saying 'work at home', and we've done that I think in six countries... or we have to house them temporarily in hotels," he said.
"The time has come to press very hard on those governments... It is their duty to make all the security available (to UN personnel)."
At least 41 people died in last month's two bombings in Algiers. Most of those killed in the attack on the UN were Development Programme staff.
The UN has announced that it will set up an outside panel to investigate the attacks and UN security around the world.
Algerian Prime Minister Abdelaziz Belkhadem was quoted in a government newspaper on Tuesday as saying that the UN probe was a "unilateral measure" and was unwelcome.
He said Algeria had "done its duty" in terms of last month's attacks.
But Mr Dervis said he was "sure" that Algeria had been consulted, and a spokeswoman said that UN chief Ban Ki-moon had talked to Mr Belkhadem about the panel.