The 26-year-old left Lazio last month as a free agent when he won an arbitration case against the Rome club, who had omitted him from their squad for five months because he asked for a move.
"The player is contracted to the club until June 30, 2014," a statement from the Serie A leaders said.
Pandev first signed for Inter as a teenager from Macedonia's FK Belasica in 2001 but failed to break into the first team and left for Lazio in 2004 where he established himself as one of Serie A's top strikers.
He became disillusioned with Lazio's mid-table struggles and asked to leave in the close-season, knowing he had just one year remaining on his contract.
Lazio president Claudio Lotito took a hard line, refusing to sell Pandev and banishing him from the team, but in the end he lost the battle in the sporting courts and the striker left for nothing.
Despite having not played a league game since May, Pandev could make an immediate debut for the Italian champions given Cameroon striker Samuel Eto'o is away at the African Nations Cup and David Suazo has been loaned to Genoa.
With the Pandev saga over, media reports say Lazio will sign Genoa forward Sergio Floccari on-loan after the former Atalanta player struggled to fit into Gian Piero Gasperini's side.
Speculation has also been rife that Inter want Lazio full-back Aleksandar Kolarov but Lotito has said he is not for sale.
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