Two British journalists have been held in Yemen accused of illegally entering the country.
Officials said the pair, along with two Americans, were taken into custody on Sunday.
They did not identify the organisations the four individuals work for or explain the circumstances of their arrest.
Yemen is continuing to be rocked by unrest.
Protesters demanding the removal of long-time president Ali Abdullah Saleh been staging daily demonstrations in the capital Sanaa and elsewhere for weeks.
The government has used violence against the protesters.