By Aaron Maasho

ADDIS ABABA (Reuters) - Ethiopia's intelligence agency said on Monday it had 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 accused of having links to militants in neighboring Somalia, where Ethiopia has deployed troops to support Mogadishu's battle with al Shabaab and its six-year insurgency.

The would-be kidnappers sought to abduct foreign employees of the U.N. World Food Programme and United Nations Development Programme from 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.

The agency did not mention when the suspects were caught or where the alleged plot was meant to have taken place.

Several U.N. agencies and other humanitarian organizations 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 crackdowns.

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 militants in January of preparing strikes on political and economic targets in Ethiopia.

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)