The UN has warned peacekeeping forces operating under its banner to obey strict rules on sexual conduct.
The UN has troops stationed in several African countries
UN deputy head Louise Frechette said soldiers would be punished if they had sex with minors or prostitutes or if they traded sex for aid or favours.
The world body has pledged to clamp down on sexual abuses following a scandal involving peacekeepers in the Democratic Republic of Congo.
Ms Frechette is touring UN peacekeeping operations in west Africa.
She made her remarks while visiting Liberia, the first stop on a tour that also takes in Sierra Leone and the Ivory Coast.
Liberia hosts some 15,000 blue helmets - one of the UN's largest deployments.
The UN Deputy Secretary-General said no cases of wrongdoing had been reported in Liberia - but there is a lesson to be learnt from recent developments elsewhere in Africa.
She told the BBC's correspondent in Monrovia, Jonathan Paye-Layleh, that UN soldiers involved in an exploitative sexual relationship could be sacked, deported or face a court martial.
The UN recently set up a hotline to receive complaints against peacekeepers accused of abuse.
The organisation has been trying to repair the damage to its reputation as it investigates some 150 claims of abuse - many of them involving minors - allegedly committed by UN peacekeepers in DR Congo.
A forthcoming UN report will recommend that soldiers suspected of misconduct face court martial in the country where the claim is made, the Associated Press news agency reports.
The move is designed to increase accountability among soldiers serving the UN abroad, who - under present rules - must be sent back home in order to face trial for alleged crimes.