A second Siberian tiger released by Russian President Vladimir Putin in the Far-Eastern Amur region in June has crossed the border into China, Russian media quoted a local environmental official as saying on Wednesday.

Viktor Serdyuk said the tiger, named Ustin, was roaming along the Amur River, or Heilongjiang River in China, some six or seven kilometers away from the border, Russian news agency TASS reported.

He added that Ustin may turn back any time as he had already done on Saturday.

Ustin is one of three Siberian tigers that Putin helped release into the wild in May and they all wear a tracking collar. Before him, Kuzya crossed the Russian border into China in early October and was spotted in the Taipinggou national reserve in Heilongjiang Province.

Chen Zhigang, the director of the Taipinggou national reserve, said Thursday that they had taken pictures of Kuzya and heard the news that Ustin is also on Chinese soil, according to news portal thepaper.cn.

The reserve is known for its biodiversity and is home to a host of animals including deers and wild boars that the tigers can prey on, said Chen. "They'll be fine here even if their survival abilities are not very strong."

Russia had asked China to look after Kuzya and China has launched a protective monitoring mechanism. Environmentalists had also expressed concerns that the tiger might be trapped or hunted by humans.

China's Criminal Law states that those who illegally hunt endangered species including the Siberian tiger could be sentenced to over 10 years in prison.