BEIJING (Reuters) - China's top diplomat will visit Vietnam this week, China's Foreign Ministry said on Tuesday, amid an increasingly ugly spat over a Chinese oil rig in the disputed South China Sea.

China's State Councilor Yang Jiechi, who outranks the foreign minister, will visit Hanoi on Wednesday, ministry spokesman Hua Chunying said at a regular briefing.

It will be the highest-level direct contact between the two sides since the rig began its operations in May.