The trial of 24 people accused of links to the 2013 assassination of prominent Tunisian opposition figure Chokri Belaid opened briefly Tuesday but was postponed until October 30, a prosecution spokesman said.

"At the request of the plaintiff and the defense of the accused, the tribunal has decided to postpone the trial to October 30," Sofiene Sliti told AFP.

British police on Tuesday launched a major counter-terror exercise in London partly influenced by the Charlie Hebdo attacks in Paris in January, just days after an Islamist gun massacre in Tunisia.

The exercise including all emergency services also comes ahead of the 10th anniversary commemorations of the July 7, 2005 attacks on London's transport system, when four suicide bombers killed 52 people.

Tunisia's president has admitted security services were not prepared for last week's jihadist beach massacre, as authorities warned the country is likely to lose more than half-a-billion dollars in tourism revenues.

Friday's carnage -- which saw a jihadist gunman kill 38 people, mostly British holidaymakers, at a seaside resort -- was the second attack on tourists in Tunisia claimed by the Islamic State group in just three months.

Israel deported Tunisian ex-president Moncef Marzouki and European parliament member Ana Miranda on Tuesday after they took part in a flotilla seeking to defy its Gaza blockade, an official said.

"The (former) president of Tunisia and the Spanish lawmaker flew this morning. There are another 14 who have begun the expulsion process," a spokeswoman for Israel's immigration authority told Agence France Presse.

A university student and fan of breakdancing who worked part-time to fund his studies, Seifeddine Rezgui seemed like a normal young Tunisian man.

So when the 23-year-old was identified as the jihadist gunman behind Friday's massacre of 38 people at a seaside resort, many of his countrymen were left in shock.

Tunisia said Monday it had made its first arrests after a beach massacre that killed 38 people, as European officials paid tribute to victims of the country's worst jihadist attack.

British Home Secretary Theresa May, speaking at the scene of Friday's gun attack at a Tunisian holiday resort, vowed that "the terrorists will not win" after London warned that Britain's death toll could rise to "around 30."

He was dressed like a tourist, but his intentions were deadly. Witnesses said Sunday the gunman who mowed town tourists at a Tunisian beach smiled as he pulled the trigger.

Armed with a Kalashnikov assault rifle, the man who massacred 38 people at a popular beach resort on Friday embarked on a murderous rampage witnesses say lasted more than 40 minutes.

The U.S. military has repatriated two Tunisian men who were brutally interrogated in a secret CIA prison and held in Afghanistan for more than a decade, the Pentagon said Sunday.

Ridha Ahmad al-Najjar and Lutfi al-Arabi al-Gharisi were flown home on June 15, officials said. 

Six people remained in "serious condition" in hospital on Sunday two days after a mass shooting at a beachside hotel in Tunisia that left 38 people dead, the hotel's Spanish management said.

"The hotel management is in permanent contact with local hospitals checking on the condition of the wounded who are still hospitalized," the RIU group, which runs the Riu Imperial Marhaba Hotel, said in a statement.

Tunisia said Sunday it would arm tourism police and deploy hundreds of reinforcements as authorities moved to boost security after a jihadist gunned down 38 people at a seaside resort.

Police on horseback and quad bikes patrolled the beach at Port El Kantaoui north of Sousse where the worst jihadist attack in Tunisia's history took place on Friday.