BRUSSELS—Belgian prosecutors say they are investigating whether two brothers trafficked antiquities that had been taken from Syria, escalating Belgium’s role in an international probe into the prominent dealers of ancient art.
Law enforcement and intelligence officials in the U.S. and elsewhere say antiquities have been looted from war-torn Syria and Iraq on a massive scale. But investigations demand patience, they say, because such artifacts take time to surface and confirming objects’ provenance can be difficult.
In January 2016, Belgian customs authorities seized two bas-reliefs sent by Phoenix Ancient Art SA to the Brussels Antiques & Fine Art Fair, or Brafa, according to the fair’s spokesman. The investigation begun by customs has since been taken up by Belgian prosecutors.
A spokesman for Belgium’s federal prosecution service said recently it was investigating two brothers, identified only as Ali A. and Hicham A. under rules barring prosecutors from releasing suspects’ full names unless charges are laid.
“It’s an ongoing investigation in close cooperation with Swiss authorities about the export of illegally obtained artifacts from Syria,” said the spokesman, Eric Van Der Sypt, adding Belgium’s effort was part of a Swiss prosecutors’ larger investigation.
A Belgian official familiar with the matter said the probe centers on Ali and Hicham Aboutaam, two pre-eminent antiquities dealers who manage Phoenix Ancient Art, according to the company’s website.
Neither man has been charged with wrongdoing in the investigations.
A spokesman at Geneva’s public prosecutor, asked to confirm whether Swiss prosecutors were investigating Phoenix Ancient Art, said the office was “conducting a procedure for suspicion of concealment and violations of the Federal Law on the International Transfer of Cultural Property.” That law is used in Switzerland to prosecute cases of alleged art trafficking. The spokesman declined to specifically name the subject of the investigation or to answer further questions.
The Wall Street Journal reported in May 2017 that Swiss, French and Belgian authorities were looking into whether the brothers had handled Syrian and Iraqi objects looted under the auspices of the extremist group Islamic State.
Didier Bottge, a lawyer acting for the Geneva arm of Phoenix Ancient Art, said his client hadn’t been contacted by Belgian authorities. He also said the Swiss “procedure” concerned the law on the international transfer of cultural property and a probe into value-added tax.
“My client formally denies being involved in ‘Syrian art trafficking,’” he said in an email.
Richard Emery, a lawyer acting for Hicham Aboutaam, in March described reports of his client’s alleged involvement with looted antiquities as containing “fake facts and implying wrongdoing where none exists” and said no authorities had contacted his client.
“My client remains anxious to cooperate with any investigators who contact him; none has,” he said. He also said he couldn’t corroborate information provided by the Journal about the Swiss and Belgian investigations. “The ‘spokespersons’ whom you cite will not confirm to us that they said what you say,” he said.
The Belgian investigation is one of the first publicly acknowledged probes into allegations of art trafficking from current war zones. Separately, in an unrelated case, Spanish police in March said they were holding two Spanish citizens suspected of trading in antiquities from Libya looted by groups linked to Islamic State.
The Belgian official familiar with the investigation said customs authorities seized the objects to establish whether they were extracted from Syria after 2011, when the war broke out there.
In early 2017, Belgium’s financial-investigation unit notified the federal prosecutor that the seized objects could be part of a case of terror financing, this official said.
“We are totally against dealing in stolen art,” Ali Aboutaam said in a February interview. He described the Belgian authorities’ suspicion that the objects seized in Belgium came from a part of Syria held by Islamic State as “total bullshit.”
He said the two seized artifacts had been traded in Europe before 2011.
A United Nations convention bans the import, export and transfer of illicit cultural goods. In 2015, amid reports of looting by Islamic State, the U.N. Security Council specifically banned all trade in artifacts “illegally removed” from Iraq since Aug. 6, 1990, and from Syria since March 15, 2011.
Mr. Emery said in his emailed response that his client, Hicham Aboutaam, hadn’t been involved in buying or displaying the objects seized in Belgium.
The items “you cite have no connection to Syria or even looted goods from any country,” he said.
Hicham Aboutaam filed a libel suit in July in the U.S. against Dow Jones, the publisher of the Journal, challenging the Journal’s May 2017 report.
A Dow Jones spokeswoman said the article was “thoroughly reported, fair and wholly accurate,” adding that the company “will mount a robust defense” to the lawsuit.
Mr. Emery and Mr. Bottge said French authorities hadn’t contacted their clients.
Ali Aboutaam’s Geneva gallery and Mr. Emery’s office emailed the Journal several documents they said proved the objects confiscated in Belgium were traded before 2011.
The documents included two auction prospectuses showing an inscribed marble tabletop put up for sale at a French auction in 2007 and at a German auction in 2010. Mr. Emery directed the Journal to a photograph on Phoenix Ancient Art’s website about the 2016 Brafa fair, showing a marble tabletop among other pieces.
Ali Aboutaam said the second confiscated item could be a contemporary counterfeit, meaning it wouldn’t have been excavated from Syria after 2011. He said he thought at the time it was sent to Brafa that “there was a chance that it could be fake.” Mr. Emery said that object appears to be a recent forgery.
Belgian authorities examined all documents submitted by Phoenix Ancient Art before opening the probe, according to the Belgian official.
— Georgi Kantchev contributed to this article.
Write to Valentina Pop at valentina.pop@wsj.com and Alistair MacDonald at alistair.macdonald@wsj.com