Sovereign immunity — Foreign States and State-owned corporations — Attachment and execution — Pre-judgment attachment of property belonging to foreign State or its agencies and instrumentalities — Foreign Sovereign Immunities Act 1976 — Whether express waiver of immunity required for pre-judgment attachment — Treaty of Amity, Economic Relations and Consular Rights, 1955, between United States and Iran — Whether amounting to waiver — Iranian Assets Control Regulations — Scope and nature — The law of the United States