Iranian state television says Tehran will file a lawsuit against the U.S. and Britain for allegedly supporting a group responsible for a mosque explosion last month that killed 14 people.

Monday's report quotes Iranian judiciary spokesman Ali Reza Jamshidi as saying Tehran will pursue the case at an "international level" because the U.S. and Britain allegedly supported the group "politically and financially." Iranian officials have alternated over whether the April 12 blast in the southern city of Shiraz was an attack or an accident. Iranian officials said Thursday an unnamed group connected to the U.S. and Britain carried out the attack.

Iran has repeatedly accused both countries of backing groups to destabilize the government. They have denied the accusations.