Chea Sim, president of the ruling Cambodian People's Party (CPP), returned home on Thursday after staying in Thailand for medical treatment for 10 days.
Witnesses said there was no reception for the CPP president at the Phnom Penh International Airport and reporters were denied access to ask him any questions.
Chea Sim left the country abruptly on July 13, causing a lot of confusion and suspicion.
The media in Cambodia suggested there was split within the CPP and Chea Sim was forced to leave the country because he refused to sign the controversial "block vote" bill into law.
CPP denied there was any party rift, claiming that Chea Sim had health problems and needed a medical treatment in Bangkok