Prime Minister Gordon Brown called on Zimbabwe on Thursday to admit international rights observers and the U.N. rights envoy for the country's run-off presidential election on June 27.

"We will work with all countries to make sure that these elections, which are now being conducted in a spiral of violence, can be free and fair," Brown told a joint news conference after talks with French President Nicolas Sarkozy.

"I appeal to the Zimbabwean government to admit international rights observers as well as the U.N. human rights envoy, so that we can be satisfied that any elections that take place, if they are to be legitimate, can be free and fair."

President Robert Mugabe lost the first round vote to opposition leader Morgan Tsvangirai on March 29, but the latter fell short of the outright majority needed to avoid a second round, according to official results.

Mugabe is accused by opponents, Western countries and human rights groups of orchestrating a campaign of killings and intimidation to keep his hold on the once prosperous country, its economy now in ruins. Mugabe blames violence on his foes.