There are a variety of sources of international human rights law, but very few of them are enforceable by individuals in a binding judicial forum.
For example, the UN Declaration of Human Rights is not enforceable in the United States or most other signatories by individuals. Similarly, the decisions of the Inter-American Commission on Human Rights are not enforceable in U.S. courts.
There is not any right, whether or not two nations are at war with each other, for individuals of each nation to right to travel to the other when necessary.
I can think of only four such cases right off:
The Council of Europe enumerates a set of human right that member nations agree to enforce in their domestic courts with appeal available from a highest domestic court to the European Court of Human Rights.
The European Union establishes rights of citizens of member states to travel, including for employment to other member nations, to vote in local elections where they reside in other member nations, and to be free of certain barriers to international trade when that trade is between member nations, all rights that would be enforced in domestic courts after adoption by a member state's legislative body.
The International War Crimes tribunal tries and punishes certain individual war criminals, once they can be apprehended by participating states in the wake of genocidal type activity usually in connection with counterinsurgency operations by government officials. This does not afford an individual any enforceable legal rights, however.
The Geneva Conventions create certain rights for civilians in war (e.g. not to be targeted without military justification) that nations that adhere to them are supposed to follow, and that a member state's courts might even enforce.