Beijing's Foreign Ministry representative in Hong Kong has accused the United States of "meddling" in the city's internal affairs and warned Washington not to hamper Sino-US relations after US Vice-President Joe Biden met two heavyweight pan-democrats from Hong Kong. Anson Chan Fang On-sang, the former chief secretary and the convenor of pro-democracy group Hong Kong 2020, and Martin Lee Chu-ming, founding chairman of Hong Kong's Democratic Party, met the US politician on Friday. They told him that the central government has been "tightening its controls" over the city and voiced fears that only candidates "hand-picked" by Beijing would be allowed to run in the 2017 chief executive election. In the question-and-answer format on the website of the Office of the Commissioner of the Foreign Ministry in Hong Kong, the spokesman for the office said: "Hong Kong affairs are China's internal affairs. We firmly oppose any countries meddling in the city's internal affairs in any way." He added: "Hong Kong is now in a sensitive political reform period. [We] would hope the US would be cautious of their words and actions regarding Hong Kong affairs and not let Hong Kong issues impede Sino-American relations." The White House meeting came a day after the pair met the Democratic Party leader of the US House of Representatives, Nancy Pelosi, in Washington. During their discussion with the vice-president, Chan and Lee also expressed concern over press freedom in the city, saying that Beijing was pressuring advertisers to shun media critical of the central government. In response to the remarks, Beijing's Foreign Ministry representative in Hong Kong commented that the city "has successfully implemented 'one country, two systems' since the handover for 17 years" and its residents enjoy "unprecedented democracy and freedom". Chan and Lee will be visiting Canada this week.