London Economic Summit Conference Declaration on International Terrorism
1. The Heads of State and Government discussed the problem of international terrorism.
2. They noted that hijacking and kidnapping had declined since the Declarations of Bonn (1978), Venice (1980) and Ottawa (1981) as a result of improved security measures, but that terrorism had developed other techniques, sometimes in association with traffic in drugs.
3. They expressed their resolve to combat this threat by every possible means, strengthening existing measures and developing effective new ones.
4. They were disturbed to note the ease with which terrorists move across international boundaries, and gain access to weapons, explosives, training and finance.
5. They viewed with serious concern the increasing involvement of states and governments in acts of terrorism, including the abuse of diplomatic immunity. They acknowledged the inviolability of diplomatic missions and other requirements of international law: but they emphasized the obligations which that law also entails.
6. Proposals which found support in the discussion included the following:
—closer co-operation and co-ordination between police and security organizations and other relevant authorities, especially in the exchange of information, intelligence and technical knowledge;
—scrutiny by each country of gaps in its national legislation which might be exploited by terrorists;
—use of the powers of the receiving state under the Vienna Convention in such matters as the size of diplomatic missions, and the number of buildings enjoying diplomatic immunity;
—action by each country to review the sale of weapons to states supporting terrorism;
— consultation and as far as possible cooperation over the expulsion or exclusion from their countries of known terrorists, including persons of diplomatic status involved in terrorism.
7. The Heads of State and Government recognised that this is a problem which affects all civilized states. They resolved to promote action through competent international organizations and among the international community as a whole to prevent and punish terrorist acts.
Ronald Reagan, London Economic Summit Conference Declaration on International Terrorism Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/261698