CAIRO (Reuters) - Egyptian security forces detained four people and have accused them of plotting to buy fuel for a pilotless aircraft for Palestinian Islamist group Hamas, security sources said on Saturday.

The sources said two of those detained were members of Egypt's opposition Muslim Brotherhood. They said the two men had given 20,000 Egyptian pounds to two other Egyptians to buy fuel and a remote control device for a small aircraft.

The sources said the small aircraft was meant to be loaded with explosives for an attack. They did not say what the target would have been.

Mohamed Mursi, a member of the Brotherhood's governing Guidance Office, said the accusations were "completely baseless" and denied any Brotherhood involvement in such a plan. Spokesmen for Egypt's interior ministry declined to comment.

The charges follow a government crackdown on the Brotherhood that led to hundreds of arrests since mid-February in the run-up to local elections on April 8. The Brotherhood boycotted these after it was largely obstructed from taking part.

The Brotherhood, which holds a fifth of the seats in the lower house of parliament, seeks an Islamic state through democratic and non-violent means.

Security sources identified the two Brotherhood men held in connection to the plane plot as al-Azhar University professor Abdel Hay al-Farmawy and Mohamed Wahdan, a doctor who has been involved in efforts to provide humanitarian assistance to Palestinians in Gaza.

Two bedouin men from Egypt's northern Sinai peninsula, not members of the Brotherhood, were also being held in the case, the sources said.

Mursi of the Brotherhood said Farmawy, a man in his sixties who he said was ill, was detained this week while Wahdan has been in detention since early February.

This month a military court sentenced 25 Brotherhood men including the group's third-in-command to jail terms ranging from three to 10 years. The court has yet to explain the verdict or clarify on what charges the men were convicted.