火上加油 (huǒ shàng jiā yóu): To add fuel to the fire (idiom) — Meaning & Stroke Order

At first the two sides had only a small misunderstanding, but he kept adding fuel to the fire from the sidelines, and in the end things became even more deadlocked.

When facing such a sensitive topic, a reporter should not add fuel to the fire but should let both sides calm down.