UNITED NATIONS, Aug. 9 (Xinhua) -- UN Secretary-General Antonio Guterres watched with concern Thursday the situation in Zimbabwe following the alleged forced return of an opposition leader seeking asylum in neighboring Zambia.

"We'll monitor the situation to see what has happened since his refoulement," Farhan Haq, Guterres' deputy spokesman, told reporters at UN Headquarters, referring to Tendai Biti, the senior opposition denied asylum in Zambia and returned to his home country.

Biti fled Zimbabwe while police were looking for him and other opposition leaders for allegedly instigating violence last week sparked by the long-time ruling party Zanu-PF winning the recent elections.

"This particular politician, Biti, was refouled from Zambia to Zimbabwe and of course we would be concerned about it if there was any mistreatment," Haq said.

Six people died in the protests following the first election after long-time, 94-year-old President Robert Mugabe was ousted in a military coup last year. Emmerson Mnangagwa, Zanu-PF leader, was elected, defeating Nelson Chamisa, Movement for Democratic Change, (MDC) leader.

"UNHCR, the UN Refugee Agency, says it is gravely concerned about reports of the forced return of a Zimbabwean asylum-seeker by Zambia to his country of origin," said Haq. "It is reported that the authorities handed him over to his country of origin today (Thursday) despite a court order to the contrary."

Published reports said that after Biti's return and a brief detention he was freed on 5,000 U.S. dollar bail

"Refoulement or forcibly returning refugees and asylum-seekers to their country of origin is a serious violation of international refugee law," the spokesman said. "UNHCR calls on Zambia to investigate this reported incident urgently."