ANKARA, Turkey (AP) — Prosecutors filed new espionage charges against Istanbul’s jailed mayor on Monday, intensifying the judicial pressure on the opposition politician seen as a top rival to President Recep Tayyip Erdogan.

The new charges against Ekrem Imamoglu stem from an investigation launched last week into alleged links between his political campaign and a businessman arrested in July for reportedly carrying out intelligence activities on behalf of foreign governments.

Imamoglu’s former campaign manager, Necati Ozkan, and journalist Merdan Yanardag were also charged.

The state-run Anadolu Agency said Imamoglu — who his already in pretrial detention on corruption charges — is suspected, among other things, of transferring personal data of Istanbul residents as part of an effort to secure international funding for his campaign.

Imamoglu rejected the accusations as “nonsense” in a statement posted on social media.

“Even the claim that I burned down Rome would have been more credible than this nonsense,” Imamoglu said. “Our struggle against this mindset that has sworn to ruin our nation’s future has now grown even stronger.”

Hundreds of supporters had rallied outside Istanbul’s main courthouse on Sunday as Imamoglu was questioned by prosecutors. It was the first time Imamoglu had left Istanbul’s Marmara Prison, on the outskirts of Istanbul, in seven months.

Critics view Imamoglu’s arrest — along with those of other mayors from the main opposition Republican People’s Party, or CHP — as part of a broader crackdown on the opposition, which made significant gains in last year’s local elections. Several CHP-run municipalities have faced waves of arrests throughout the year.

Imamoglu’s arrest in March sparked nationwide protests. Erdogan’s government insists that Turkey’s judiciary is independent and that the investigations are strictly focused on corruption.