MUFJ Bank and Mizuho Bank plan to halt all Iran-linked transactions as soon as August, following the United States' decision to reimpose sanctions against Tehran, sources close to the matter said Thursday.

The banking units of Mitsubishi UFJ Financial Group Inc. and Mizuho Financial Group Inc. have both started informing their customers of the plans, the sources said.

Under the U.S. sanctions, to be implemented in stages starting in August, banks with Iran-related transactions would face substantial restrictions regarding their business with U.S. financial institutions.

On May 8, U.S. President Donald Trump withdrew Washington from the 2015 Iran nuclear deal as he pledged to reinstate U.S. sanctions on Tehran.

Under the deal struck between Iran and six major powers -- Britain, China, France, Germany, Russia and the United States -- Tehran agreed to curb its nuclear activities in exchange for the lifting of crippling economic sanctions.