BUDAPEST: Hungary fiercely defended Wednesday a jail term given to a Syrian-Cypriot man for his role in a border riot last year, a verdict criticised by both Washington and Amnesty International.

Ahmed Hamed, 40, was jailed for 10 years last week by a court in Szeged, southern Hungary, for committing "illegal border crossing and an act of terror while participating in a mass disturbance".

Prosecutors had accused him of using a megaphone to stir up violence and of throwing "three solid objects" at police when several dozen migrants tried to cross into Hungary from Serbia on Sept 16, 2015, a day after the border was sealed with razor wire.

Hamed's verdict was criticised Tuesday by the US State Department which it said was "based on a broad interpretation of what constitutes 'terrorism'".

Hungary should conduct a "transparent investigation, with input from independent civil society groups," deputy department spokesperson Mark Toner said in a statement.

But Hungarian authorities rejected the criticism on Wednesday, with foreign ministry spokesman Tamas Menczer calling Toner's remarks "outrageous and unacceptable".

"To attack the Hungarian border, for hours to direct attacks against Hungarian police protecting the border is a serious crime which carries a serious punishment," Menczer said in a statement.

"It is strange that the State Department which regularly lectures the world about the separation of powers is now calling on a government to intervene in a court's business," Menczer said.

During the clashes at the Roszke checkpoint Hungarian riot police used tear gas and water cannon to force the group of migrants back onto Serbian territory.

Around 15 police and 100-150 migrants were injured, including women and children.

A resident of EU member Cyprus for around a decade, Hamed told the court that he was escorting his elderly parents from Syria to Germany.

He said that he had used his knowledge of English to mediate by megaphone between the migrants and the riot police.

His lawyer said there was also no evidence that Hamed had injured anyone, and said the verdict will be appealed.

"Throwing stones and entering a country irregularly does not constitute terrorism and cannot justify this draconian ruling," Gauri van Gulik from rights group Amnesty International said afterwards.

The verdict was "correct" however, insisted Prime Minister Viktor Orban last week.

"We told them the situation in advance, the country was full of billboards," he said, a reference to a nationwide poster campaign last year warning migrants against breaking the law and widely seen as connecting migrants to crime and terrorism.

In July, 10 other mostly Syrian and Iraqi migrants were given between one and three year jail terms for illegal border crossing during the same disturbances. — AFP