China's education ministry has ordered colleges to cut ties with Oxfam and prevent it from recruiting on campuses, accusing its Hong Kong branch of a hidden political agenda.

While Beijing is often anxious about NGOs, the British-founded agency has been working on the mainland for more than two decades in co-operation with the government. It is unclear what prompted the surprise decision.

A notice attributed to the education ministry said the Hong Kong branch of Oxfam, which oversees operations on the mainland, was a "non-governmental organisation seeking to infiltrate" the mainland .

It described the group's head as a "stalwart of the opposition faction", according to the South China Morning Post, which saw the notice on a website run by Minzu University in Beijing. The notice, dated 4 February, also said: "All education departments and institutions of higher education must raise their guard and together recognise and take precautions against the unfriendly intentions of Oxfam Hong Kong's recruitment of college volunteers." The notice has since been removed. The newspaper said two other university websites carried what appeared to be summaries of the notice.

The Post added that the chairman of Oxfam Hong Kong, Lo Chi-kin, was a member of the territory's Democratic party, which advocates reforms including direct elections for the legislature.

Matthew Granger, a spokesman for Oxfam International, said: "We have had no notification from the ministry of education or officials of any problem. We have suspended the programme while we try to clarify whether there is a problem."

The notice appears to refer to an internship programme started in 2006 that has placed 40 students working at NGOs into sectors such as supporting migrant workers.

Charlotte Kong, communications manager of Oxfam Hong Kong, said the project was part of its broader attempts to contribute to the development of civil society.

Kong said in a statement: "We believe it is in line with the central government's policies encouraging more students to enter the field of social work. In the past four years we never received any warning that this programme was sensitive.

"With the economy growing fast and society becoming more advanced, we are sure NGOs and civil societies are becoming an important contributor to China's development."

The organisation said the personal politics of Oxfam Hong Kong's board members and employees had no influence on its work.

Oxfam has five offices on the mainland and its work has ranged from education projects and advocacy on climate change to helping communities in Sichuan province recover from the 2008 earthquake.

Although some officials have sought to encourage the development of NGOs and welcomed their potential to complement the work of the state, Beijing remains wary of the country's emerging civil society and its potential to challenge the government. Domestic groups often register themselves as companies because of the difficulties in establishing themselves legally. Foreign organisations also operate under tight restrictions.

But Oxfam would not have been able to run the scheme for four years without some kind of agreement with officials.