VIENNA (Reuters) - China and Russia are set to join four Western powers in voicing deep concern about Iran's atomic activities this week and pressing it to cooperate with a stalled inquiry by the U.N. nuclear watchdog, diplomats said on Tuesday.

A draft statement by the six world powers, expected to be delivered at a meeting this week of the 35-nation board of the International Atomic Energy Agency, says it is "essential and urgent" for Iran to engage with the IAEA, they said.

The statement - which diplomats said had yet to be formally approved by all the six capitals - appeared intended to signal continued big power unity in a decade-old dispute over Iran's nuclear program.

The West suspects Iran is seeking the capability to make nuclear weapons. Iran denies this.

(Reporting by Fredrik Dahl; Editing by Kevin Liffey)