Cambodian police arrested eight people Thursday for displaying portraits of US President Barack Obama next to the word "SOS" on their roofs ahead of his much-anticipated visit to the nation.

The stunt was carried out by residents living near Phnom Penh airport in protest at their threatened eviction, a local human rights group said, in the latest of a slew of bitter land disputes across the impoverished country.

The charges against the six women and two men were not immediately clear.

"They put Obama's picture on their roofs and painted 'SOS' next to it," said national police spokesman Kirt Chantharith, adding "we are questioning them about their reason for doing this".

Obama will become the first sitting US president to visit Cambodia when he flies into the capital next week to attend the annual East Asia Summit with regional leaders.

The detentions are the latest example of officials trying to suppress criticism or polish Cambodia's image ahead of the high-profile event, said Ou Virak, president of the Cambodian Centre for Human Rights.

"It says quite a bit about this government and its intention to put on a good face in front of the international community," he told AFP.

Over 180 families living near the airport have been served with eviction notices to make way for its planned expansion and are demanding fair compensation.

Forced evictions across the country have displaced thousands of families and prompted a number of protests and violent clashes between residents and armed security forces.

In preparation for the summit, city officials have rounded up nearly 100 beggars, drug addicts, sex workers and street vendors to make the capital "beautiful" and "for public order", municipal hall spokesman Long Dimanche said.

Many were sent to social affairs centres -- effective detention centres much criticised by rights campaigners in the past -- while some street children were taken to local charities, he added.