The delegation included three Khmer monks who had spent about one year in jail each in Vietnam.
The agreement, which is expected to spur trade, tourism and other activities in Cambodia.
China has pledged to provide military aid, including more than 250 trucks, exceeding a previous aid scrapped by the US.
The land dispute in Kampong Speu underscores the difficulties arising throughout Cambodia.
Un Sokhom was the editor in chief of the Neak Prayuth newspaper until he fled to the US in 2004 in fear of his safety.
Organizers of the Cambodian Confederation of Unions had planned to show the film, which questions the motives behind the 2004 murder.
Cambodia has sought similar deals in Middle Eastern countries like Kuwait and Qatar, where food shortages are a concern.
The Ministry of Foreign Affairs issued an unexplained letter to embassies on Tuesday.
The phone purchase was just one example the Nobel Prize laureate gave as he described his country’s battle against corruption.
The Khmer Rouge ruled for only four years, but it has taken more than 30 to relieve the trauma, he said. And it’s still there.
Prime Minister Hun Sen on Wednesday said he was committed to fighting terrorism, with the participation of Cambodian citizens.
Mu Sochua, a member of the Sam Rainsy Party, was fined for remarks made in connection with a lawsuit against Prime Minister Hun Sen.