BEIRUT - Lebanon's central bank governor Riad Salameh said on Tuesday that the institution's exchange platform, Sayrafa, would begin selling unlimited amounts of U.S. dollars in a bid to halt the spiralling devaluation of the Lebanese pound.

Salameh set the new Sayrafa rate at 90,000 Lebanese pounds per dollar. The Lebanese pound's parallel market rate had weakened from roughly 121,000 to the U.S. dollar on Tuesday morning to 140,000 by the afternoon, and began rising in value immediately after the decision was announced.

The central bank had re-valued the official rate to 15,000 pounds per U.S. dollar on Feb. 1 - already a 90% devaluation from the longtime peg of 1,507.5.

Unifying multiple exchange rates is one of several steps sought by the International Monetary Fund for Lebanon to clinch a $3 billion aid package that would help it to emerge from the meltdown.

(Reporting by Laila Al Bassam, Writing by Maya Gebeily, Editing by Andrew Heavens, William Maclean)