One of Israel's most prominent opposition politicians has called for an investigation into the alleged abuse of activists from the Global Sumud Flotilla, which was intercepted by the Israeli military in the Mediterranean last week.Many of the activists, including Australians, have levelled serious allegations against Israeli authorities, ranging from reports of beatings to sexual assault."Abuse is never a good idea," Yesh Atid leader Yair Lapid told journalists in Jerusalem."This is the difference between us and the terror organisations and the terrorist countries that surround us. Democracy comes with a price, and we should pay the price."Some of the treatment of the flotilla members was highlighted in a video posted by Israel's far-right national security minister, Itamar Ben-Gvir.Israeli vessels approaching the flotilla last week. (Supplied: Global Sumud Flotilla)Countries summon Israeli ambassadors to their capitalsThe footage showed activists being pushed and dragged by officers, kneeling on the ground in stress positions with their hands zip-tied behind their backs, and the minister taunting them."What he did was inexcusable and should be investigated," Mr Lapid said."Why is it that nobody around him said, 'OK, you're not allowed to do this?'"The video of Mr Ben-Gvir, who has responsibility for the nation's police and prison services, sparked global condemnation.A number of countries, including Australia, summoned the Israeli ambassadors in their capitals for questioning over the incident.Israeli Prime Minister Benjamin Netanyahu also rebuked Mr Ben-Gvir, who is the leader of the far-right Otzma Yehudit Party, which translates to "Jewish Power".Mr Netanyahu appointed him to the crucial ministry as part of his coalition negotiations, despite Mr Ben-Gvir's numerous criminal convictions, including for terrorism offences.The Israel Defense Forces (IDF) denied the allegations of mistreatment and abuse."IDF orders require respectful and appropriate treatment of the flotilla participants on the intercepted vessels," it said in a statement."No specific incidents of deviation from these binding procedures are known within the IDF."Bid to unseat NetanyahuMr Lapid is highly critical of Mr Netanyahu and is trying to unseat him at the upcoming Israeli elections, which must be held by October.Israeli media is speculating that the election could be set for September 15, once legislation to dissolve the Knesset is passed.A former prime minister himself, Mr Lapid has recently announced a joint ticket with Naftali Bennett, another former leader of Israel.By banding together, the pair are hoping their parties will be in a stronger position to topple the Netanyahu coalition.Mr Lapid has conceded it would be unlikely that he would be prime minister in any new coalition, with that role to be taken by Mr Bennett.Although he questioned the treatment of the activists, Mr Lapid said it was appropriate for the IDF to intercept the flotilla, which was trying to break Israel's almost two-decade maritime blockade of Gaza.Interception of 'propaganda mission'The Australian government has criticised the video posted by Mr Ben-Gvir but has not commented on the interception mission itself, the legality of which has been called into question by a number of experts."Every country on Earth has the right to prevent people from coming into closed military zones," Mr Lapid said."Gaza right now is a closed military zone, and therefore they cannot just sail in on a propaganda mission. So I think it was the right thing to do."Mr Lapid, a former journalist, labelled political support for the surge in settler violence in the West Bank a "disgrace".He was asked about whether the settlers, whose presence in the West Bank is considered illegal under international law, were being propped up by the Israeli military."I'm more worried about the support from within the government that creates the ability of support within the army and the police," Mr Lapid said."How come it didn't happen in our time when we were in government? It didn't happen because it was so obvious that we will not allow it."Right now, the fact that the minister in charge of the police is a known supporter of that kind of settler violence is creating part of this wave."So what we need is a different way of governing this, a different of policing this. "These are criminals, … [these are] terror acts and should be treated as such. "Israel is presumably very good at preventing terror from happening."