The European Central Bank earned 7.8 billion euros ($9.2 billion) of interest in 2012-16 on Greek debt it bought to shore up the fragile nation, a figure promising renewed tensions with eurozone partners.

Some of the funds are still in limbo, despite the fact that any profits from bonds owned by the ECB and its 19 national counterparts are supposed to be returned to the Greek state.

ECB chief Mario Draghi revealed the sum in a letter to a Greek European Parliament lawmaker Tuesday.

Decisions about what happens to the cash "do not fall within the remit of the ECB", Draghi recalled, lying instead with the single currency's member states.

Eurozone governments agreed in 2012 to send the profits reaped by their central banks from Greek bonds -- which would usually end up into finance ministries' coffers -- to Athens as part of the country's second bailout programme.

The 7.8 billion euros of interest built up on bonds bought by the ECB and member countries' central banks under a scheme known as SMP, through which around 35 billion euros of Greek debt was purchased.

Greece's central bank also bought its own government's bonds under a separate programme known as ANFA.

Some 4.3 billion euros of profits from SMP and ANFA made between 2012 and 2016 have been transferred to Athens, European economics and finance commissioner Pierre Moscovici told lawmakers in Brussels last month without offering a breakdown of how much came from each programme.

But cash from central banks outside Greece stopped flowing in 2014, he added.

Around 1.8 billion euros dating from 2014 is also locked away in an account intended to pay off the country's debt as it falls due -- if it followed through with tough economic reforms demanded by its creditors.

That arrangement broke down in 2015, when eurozone finance ministers -- the so-called "Eurogroup" -- decided to freeze transfers to Athens during a standoff with Greek Prime Minister Alexis Tsipras.

Happy with more cooperation from the Greek government, the Eurogroup said at the end of June that it would reinstate the payments -- but only dating back to the start of 2017.