* UN calls for halt in Sri Lanka fighting
* UN says both sides may have committed war crimes
* "Ruthless disregard" for civilians
GENEVA, March 13 (Reuters) - Both sides in Sri Lanka's conflict may have committed war crimes and must suspend fighting to let thousands of civilians escape, United Nations High Commissioner for Human Rights Navi Pillay said on Friday.
Warning that the loss of life may reach "catastrophic levels", she urged the government and Liberation Tigers of Tamil Eelam (LTTE) rebels to suspend hostilities to allow evacuation of up to 180,000 civilians trapped on the northeastern coast.
Pillay said the government had repeatedly shelled the designated "no-fire" zones for civilians and also cited reports that the separatist guerrillas were holding civilians as human shields and had shot some as they tried to flee.
"Certain actions being undertaken by the Sri Lankan military and by the LTTE may constitute violations of international human rights and humanitarian law," Pillay said in a statement issued in Geneva.
"The world today is ever sensitive about such acts that could amount to war crimes and crimes against humanity," added the former U.N. war crimes judge, who grew up in a poor Indian neighbourhood in Durban as a member of South Africa's Tamil minority.
Sri Lanka's military has encircled the LTTE Tamil Tigers in a mere 37 sq km (15 sq miles) of the island nation's northeastern coast and is fighting to deal a death blow to a civil war that has raged off and on since 1983. [ID:nCOL467908]
More than 2,800 civilians may have been killed and more than 7,000 injured since Jan. 20, according to a range of credible sources, Pillay said. Many had been inside the "no-fire" zones.
Hundreds of children were believed to be among the dead.
"The current level of civilian casualties is truly shocking and there are legitimate fears that the loss of life may reach catastrophic levels, if the fighting continues in this way," Pillay said.
"The brutal and inhuman treatment of civilians by the LTTE is utterly reprehensible and should be examined to see if it constitutes war crimes," she said. (reporting Stephanie Nebehay; editing by Jonathan Lynn)