Sitapur (UP), Jul 8 Three persons were killed and 10 others injured when two cars collided on Sitapur-Lakhimpur Highway, police said today. 13 persons were injured in the mishap that happened late last night in Jhrekhapur locality in Hargaon area here, they said. The injured were rushed to a hospital where three succumbed during treatment, police said, adding, the condition of others is stated to be stable.