The coup against Makarios was engineered by the Greek government.

corroboratedconfidence: high

Asserted by the US Embassy in Athens, by the Turkish prime minister, and by the INR post-mortem.

Supporting and corroborating evidence

The evidence to date seems clearly to implicate Ioannides with the coup in Cyprus. It is also clear operation against Makarios was carefully planned, as declaration called 'Government of National Salvation' demonstrates.
Ambassador Tasca — FRUS 1969-76 v30 D81, Embassy Athens, 1974-07-15 · source ↗

Coup completely engineered by Greek Govt.
Bülent Ecevit (as reported by Macomber) — FRUS 1969-76 v30 D90, Embassy Ankara, 1974-07-17 · source ↗

Context

Ioannides sees one of two things happening in Cyprus. Either Cyprus will slowly drift left and become a Cuba of the Mediterranean (this drift will be caused by the Communist propaganda which is being taught in the school system), or the 80 percent Greek majority will achieve union with Greece. The one thing that cannot happen is union with Turkey.
Dimitrios Ioannides (as relayed) — FRUS 1969-76 v30 D14, Embassy Athens, 1974-06-14 · source ↗

From what I've seen so far there is no collusion between the Greeks and the Turks.
Joseph Sisco — FRUS 1969-76 v30 D80, NSC / WSAG, 1974-07-15 · source ↗