The Secretary of State.
Multiple members of the Cabinet deal with foreign relations, however Secretary of State Hillary Clinton specializes in the affairs of foreign nations
Foreign policy is policy that deals with foreign affairs.
The name of the cabinet secretary of the ministry of Foreign Affairs in Kenya is Hon. Amb. Amina Mohammed.
The Department of the Interior.
The Hon Fredrick A. Mitchell
foreign relations
Secretary of State
MI5 deals with home affairs so threats within Britons borders and MI6 deals with foreign affairs in Afghanistan etc.
Countries do not have affairs in the way you imply in your question. Countries have foreign relations with other countries and the department that deals with these relationships is called the foreign affairs department.A foreign affairs department will have relations with all countries. some of which will be ambassadorial relationships.
The State Department, under direction of the President, deals with foreign policy.
In Britain, it is the Foreign Office, headed by the Member of Parliament of the ruling party, given the title of Foreign Minister by the Prime Minister.
The secretary of state heads the state department which is charged with foreign affairs,