A rights lawyer who has defended some of China's most prominent dissidents said Friday police prevented him from meeting the visiting German Chancellor Angela Merkel.

Mo Shaoping, whose clients include jailed Nobel Peace Prize winner Liu Xiaobo, said he was invited to a reception at the German embassy to be attended by Merkel Thursday, but police arrived at his office and stopped him going.

"They were in my office for over three hours. They had no legal basis for stopping me, but they would not let me go," Mo told AFP.

"I had been invited on Monday to discuss with the chancellor China's situation concerning the law and the plight of lawyers."

Mo said police told him he was not allowed to attend the meeting due to concerns over social stability ahead of a key Communist Party meeting slated for late this year that will usher in a 10-yearly leadership transition.

The German embassy in Beijing did not immediately comment on the absence of Mo, who also defended the jailed rights lawyer Gao Zhisheng.

Merkel, who has held talks with Premier Wen Jiabao and President Hu Jintao during her visit, had said that she would raise human rights issues during her visit.

On Friday, Merkel departed for south China's manufacturing hub, where she is slated to meet Gan Junqiu, the state-backed Catholic bishop of Guangzhou, according to a German diplomatic source.

Police in China rounded up scores of human rights lawyers and activists early last year amid online calls for protests in China similar to those that toppled governments in North Africa and the Middle East.

Mo said it was not the first time police had stopped him meeting western leaders or diplomats.

Last year he was prevented from seeing French Foreign Minister Alain Juppe and Beijing-based diplomats from Germany, the Netherlands and the European Union, he said.

But he was allowed to meet US Ambassador Gary Locke in October, he said.