Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Nairobi, Kenya (CNN) -- In the worst single incident for Kenyan police in living memory, 38 officers were killed in northern Kenya over the weekend by heavily armed cattle rustlers, according to injured police reservists who were on the scene. Local media reports put the number at between 37 and 42 dead. Internal Security Minister Katoo Ole Metito would not give a total figure on how many police officers had died. Read more: Attack on Sunday school leaves child dead, others wounded The police officers were part of an operation to recover cattle belonging to the Samburu tribe that had been stolen by the Turkana tribe, according to the minister. They were ambushed in a valley when a large group of Turkana fired on police, leaving dozens dead and many injured.The officers were trying to recover stolen cattle, a security official saysThe Turkana and Samburu tribes have engaged in tit-for-tat cattle rustling operationsIt's not unusual to see cattle herders armed with automatic riflesThe security minster says the government is trying to reconcile the two communities 
 Question:The Kenyan government intervened and gave an ultimatum for the _ to return the cattle last Friday, or it would respond with force.

Turkana