Article 40 Vienna Convention on Diplomatic Relations

1.If a diplomatic agent passes through or is in the territory of a third State, which has granted him a passport visa if such visa was necessary, while proceeding to take up or to return to his post, or when returning to his own country, the third State shall accord him inviolability and such other immunities as may be required to ensure his transit or return. The same shall apply in the case of any members of his family enjoying privileges or immunities who are accompanying the diplomatic agent, or travelling
separately to join him or to return to their country.

2.In circumstances similar to those specified in paragraph 1 of this article, third States shall not hinder the passage of members of the administrative and technical or service staff of a mission, and of members of their families, through their territories.

3.Third States shall accord to official correspondence and other official communications in transit, including messages in code or cipher, the same freedom and protection as is accorded by the receiving State. They shall accord to diplomatic couriers, who have been granted a passport visa if such visa was necessary, and diplomatic bags in transit, the same inviolability and protection as the receiving
State is bound to accord.

4.The obligations of third States under paragraphs 1, 2 and 3 of this article shall also apply to the persons mentioned respectively in those paragraphs, and to official communications and diplomatic bags, whose presence in the territory of the third State is due to force majeure.

See also: Article 39 Vienna Convention on Diplomatic Relations