Lt. Gen. Shavendra Silva was appointed Chief of the Sri Lankan Army in August, eliciting criticism from the UN, the US and the European Union.
Silva commanded Sri Lanka's 58th Division during the final stages of the military campaign against the Tamil Tigers in 2009 "and successive UN investigations have implicated his division in alleged serious violations of international humanitarian and human rights law", says the UN.
According to a UN investigation, 40,000 people, many of them Tamil civil, were killed in the last days of the war.
Following his appointment, UN High Commissioner for Human Rights Michelle Bachelet said Silva's promotion "severely compromises Sri Lanka's commitment to promote justice and accountability".
On Wednesday, a UN spokesperson told American news publication Foreign Policy that the world body would ban new Sri Lankan units from deploying in its missions unless their presence was vital for ensuring the missions' security.
"We have expressed our concern to the government of Sri Lanka over the appointment of Lieutenant General Shavendra Silva to the position of commander of the Sri Lanka Army despite well-documented, credible allegations of his involvement in serious violations of international humanitarian and human rights law," said Farhan Haq, the deputy spokesman for UN Secretary-General Antonio Guterres.
"In light of this appointment, the UN Department of Peace Operations is, therefore, suspending future Sri Lankan Army deployments except where suspension would expose UN operations to serious operational risk," he added.
( With inputs from IANS )