U.S. Secretary of State John Kerry is in Cambodia where he has welcomed the Southeast Asian nation's booming economic growth but also expressed concerns about its human rights record.

Kerry met top Cambodian officials, including Prime Minister Hun Sen, as well as members of the opposition on Tuesday and discussed the possibility of a U.S.-Cambodia bilateral investment treaty.

The opposition is led by a led by a politician, Sam Rainsy, who has been in self-imposed exile since November, when an order for his arrest was issued on an old conviction for defaming Cambodia's foreign minister.

Cambodia is Kerry's second-to-go-last stop on an around-the-world diplomatic trip that began in Switzerland and took him to Saudi Arabia and Laos. He will visit China before returning home.