The building of a Turkish opposition party in Istanbul was hit by two bullets overnight, its leader said on Friday, in what she described as an attempt to scare party members ahead of landmark presidential and parliamentary elections next month.

There were no reports of anybody being hurt in the shooting, which targeted the Istanbul office of the right-wing IYI Party in the early hours of the morning.

One bullet hit the ground floor and another the third floor, IYI party leader Meral Aksener told reporters.

"This is an attempt to scare members of a political party just one month and a half before the elections. This is unacceptable. You cannot scare us but this is an insult to voters," Aksener said.

The Istanbul governor's office said the police had launched an investigation into the incident.

Video footage showed that a bullet had pierced a ground floor window where a cafeteria section is located and had lodged in a chair there.

The IYI Party is part of a six-party opposition alliance which has nominated Kemal Kilicdaroglu, leader of Turkey's main opposition Republican People's Party (CHP) as their candidate to challenge President Tayyip Erdogan in the May 14 elections.

Istanbul Mayor Ekrem Imamoglu, a CHP member, condemned the incident and Kilicdaroglu called on authorities to investigate.

"Ms. Aksener is a strong leader, you cannot scare her like that," Kilicdaroglu wrote on Twitter. "I expect the perpetrators to be caught immediately and brought to justice."

The spokesperson for Erdogan's ruling AK Party, Omer Celik, also condemned the incident.

"It is important to take a common stance against all provocations, especially with elections approaching," he said on Twitter. "We will stand against attacks on political parties as strongly as possible."

Next month's elections mark the toughest political challenge yet for Erdogan, who has led the country for two decades but has seen his popularity tumble amid an economic crisis and the impact of a devastating earthquake in southeast Turkey.

While polls show him trailing Kilicdaroglu, however, the race remains tight and campaigning is only just beginning.

(Reporting by Huseyin Hayatsever; Editing by Daren Butler and Gareth Jones)