THE HAGUE — The first foreign observers permitted by governments in Moscow and Kiev to monitor the political situation and human rights are assembling in the Ukrainian capital and will start fanning out across the troubled region on Tuesday, a spokeswoman said Sunday.

Deployment of the first 100 observers — a number that may rise to 500 during the six-month mission — was viewed by some diplomats as the first break in the crisis over Crimea since Russia sent thousands of troops into the peninsula and then annexed it last week. The annexation, considered illegal by the West, followed a public referendum in favor in Crimea on March 16.

Moscow expressly barred the monitors from Crimea, and even suggested that the mission constituted foreign recognition that the peninsula was now Russia’s — a notion swiftly dismissed in the West.

The monitors are working for the 57-nation Organization for Security and Cooperation in Europe, or O.S.C.E., which is based in Vienna and frequently used to monitor military and ethnic tensions.