The letter raised concerns about continued UK arms sales to Israel, referencing the killing of aid workers and the blockade on aid into Gaza.
Senior Foreign Office officials Sir Oliver Robbins and Nick Dyer responded by stating that civil servants profoundly disagreeing with government policy should resign.
The officials emphasized the need for a "healthy challenge" to policy but stressed civil servants' duty to implement the government's agenda.
The Foreign Office stated that it rigorously applies international law regarding the conflict in Gaza, having suspended some arms export licenses and halting negotiations on a free trade agreement.