Security forces of the Islamist group Hamas detained Palestinian political activists overnight for distributing leaflets urging them to ease up on the people of Gaza or face a possibly explosive revolt.

An official of the Popular Front for the Liberation of Palestine (PFLP) told Reuters several members were arrested late on Tuesday and set free on Wednesday.

The PFLP leaflets were the strongest public criticism yet of Hamas, which seized control of the Gaza Strip in 2007 and has been clamping down on any behavior it sees as un-Islamic, while recently levying new taxes on the 1.5 million inhabitants.

"People are under huge pressure but they are also afraid to express themselves and we took the responsibility to voice their concerns," PFLP official Jamil Mezher told Reuters.

The leaflet warned Hamas to beware increasing pressure on the people in a way that could "push the community to rebel against these practices and even to explode in the faces of those responsible."

It urged the territory's Islamist rulers to stop violating freedoms, oppressing political opponents and imposing taxes on small businesses in the enclave, whose borders with Israel and Egypt are tightly controlled.

The price of a pack of cigarettes, most of which are smuggled in via tunnels from Egypt, has been raised to cover a NIS 3 (80 cent) tax which goes to Hamas.

Another group, the Democratic Front for the Liberation of Palestine (DFLP), urged peaceful protests against Hamas taxes.

"The DFLP condemns the increase of taxes and fees ... which have led to an unprecedented rise in prices amid deteriorating economic and social conditions," it said. "We call for popular action and peace protests to stop these measures."

Israel invaded Gaza in a three-week offensive 16 months ago to force an end to rocket fire by Hamas and other groups aimed at towns in southern Israel. But the border remains tense and violent incidents involving troops and militants are frequent.

Local traders say the group is trying to patch up its depleted finances and calculate this tax will yield it about $6 million per month.

The PFLP also noted a new Hamas move to take over uninhabited housing and offer it to their members.

Economists say half the people are jobless in Gaza, which subsists on United Nations aid. They cannot leave the enclave.

PFLP leaders said they had urged Hamas in a face-to-face meeting recently to ease up.

The Hamas administration denied it had imposed any new tax and said it had only "activated a tiny section of the taxation system."

Mezher said the PFLP had plenty of testimony to the contrary from ordinary people. Many government employees said they had not yet been paid for the month of March.

Hamas Islamists are allied with Iran and refuse to recognize Israel, unlike their arch rivals in the Fatah movement, which is dominant in the West Bank and open to a peace treaty that would create a Palestinian state alongside Israel.

Prospects of the two groups reconciling to heal the split in Palestinian ranks are seen as remote.