TEL AVIV (Reuters) - Israeli police emergency lines lit up on Thursday after warplanes roared over the Tel Aviv coast, dropping anti-missile flares and performing aerobatics at a time of tension along the border with Syria.

FILE PHOTO: An Israeli Air Force F-15 fighter jet releases flares during an aerial demonstration at a graduation ceremony for Israeli air force pilots at the Hatzerim air base in southern Israel December 29, 2016. REUTERS/Amir Cohen/File Photo

It was just a rehearsal - practice flights are held every year - for the Israeli Air Force’s annual Independence Day national flypast on April 19, but no prior announcement was made.

“Many calls were received from worried citizens about noise from a squadron of planes in the Tel Aviv area,” police said in statement. “We would like to make clear they were training for the Independence Day aerial display. There’s no emergency.”

The military later issued a statement apologising for the scare and it listed locations and times of further rehearsals over the next few days ahead of the annual display, when onlookers will cram the Tel Aviv beachfront.

Under clear skies over Tel Aviv’s Mediterranean beach, two F-15 jets manoeuvred through a series of sharp turns, climbs and dives in what appeared to be a mock dogfight as the sound of their engines crackled through the streets.

On Wednesday, U.S. President Donald Trump warned Russia of imminent military action in Syria over a suspected poison gas attack, and Israel held top-level security consultations over concerns it might be a target for Syrian or Iranian retaliation.

Trump said on Thursday that a possible strike against Syria “could be very soon or not so soon at all”.

Despite the tensions, the commander of Israel’s armed forces, Lieutenant-General Gadi Eizenkot, flew to Poland on Thursday morning to take part in Holocaust Remembrance Day events.

The Israeli military tweeted a video of him boarding a plane but did not immediately say when he was scheduled to return. A source in the delegation told Reuters, however, that Eizenkot would be back by nightfall.

In Israel, sirens blared for two minutes during the morning to mark the remembrance day, bringing traffic to a standstill as motorists and pedestrians stood to honour the six million Jews killed in the Nazi Holocaust.

Civil defence authorities issued the customary notice beforehand that in the event of a real emergency, the sirens would sound in a rising and falling, rather than a constant, tone.