* Ethiopia has cracked down on al Shabaab militants
* U.N. staffers operate in Ethiopian region near Somalia
* Addis Ababa has troops in Somalia fighting rebels (Adds detail of plot from official)
By Aaron Maasho
ADDIS ABABA, March 25 (Reuters) - Ethiopia's intelligence agency said on Monday it has detained eight members of Somalia's al Shabaab Islamist militant group who it accused of plotting to kidnap U.N. workers.
The arrests were the latest in a crackdown on people charged with having links to fighters in neighbouring Somalia, where Ethiopia has deployed troops to support Mogadishu's battle against al Shabaab and its six-year insurgency.
The group wanted to abduct foreigners working for the U.N. World Food Programme and the United Nations Development Programme in Ethiopia and take them to Somalia to demand a ransom, the National Intelligence and Security Service (NISS) said.
"The eight were caught red-handed with arms as they plotted to carry out the kidnappings," NISS said in a statement.
An Ethiopian official told Reuters the group planned to carry out the abductions in a camp for Somali refugees in the Ethiopian frontier town of Dolo Ado.
Several U.N. agencies and other humanitarian organisations operate in Ethiopia's dry Somali region that borders Somalia.
The region has also been plagued by a low-key rebellion for nearly two decades, though residents now say local rebels have largely been weakened by successive government offensives.
Monday's announcement comes two months after authorities said they arrested 15 suspected militants who were accused of being trained by al Shabaab.
An Ethiopian court convicted 10 other people in January of preparing strikes on political and economic targets in Ethiopia.
Somalia's al Shabaab group has threatened to attack Ethiopia in revenge for its military interventions.
Ethiopia fought Islamist rebels in Somalia in 2006 to 2009 and sent troops back in 2011 to fight al Shabaab, opening a third front alongside Kenyan troops and an African Union (AU)mission.
The campaign in Somalia has gained ground in the past two years. Al Shabaab, which is allied with al Qaeda, withdrew from the southern port of Kismayu in September, its last major urban stronghold. (Reporting by Aaron Maasho; Editing by Edmund Blair)