Swiss justice authorities have confirmed they are investigating a World Cup TV rights contract signed off by Sepp Blatter that was sold to Jack Warner for a fraction of its true value.

Michael Lauber, the Swiss attorney general, told a news conference in Zurich that FIFA had sent prosecutors its explanation for the contract sold to the Warner-controlled Caribbean Football Union for US$600,000 (€530,000) - Warner's company later sold them on for an almost €15m profit.

Meanwhile, the US attorney general Loretta Lynch has announced fresh arrests and charges are likely as a result of the separate FBI investigations into the FIFA corruption scandal.

Lynch, speaking at the same news conference, said new charges and arrests against "individuals and entities" were anticipated.

Lauber also revealed that assets including flats in the Swiss Alps and western Switzerland had been seized by his investigators, on suspicion of being used for money-laundering purposes, and that 121 different bank accounts have been brought to the attention of the investigating task force.

In May, the US justice department announced indictments against 18 people on football-related corruption charges - four have pleaded guilty to charges.

Lynch told a news conference: "Separate and apart from the pending indictment our investigation has expanded since May. The scope of our investigation is not limited and is following the evidence where it leads.

"We do anticipate pursuing additional changes against individuals and entities."

Asked if Blatter was under investigation or if it might interfere with his travel plans - the FIFA president did not travel to the women's World Cup in Canada in June following the arrests in May - Lynch added: "I'm not going to comment on individuals and I am not able to give you information about Mr Blatter's travel plans."

The Swiss and US investigations remain separate, and Lauber's disclosure that Swiss authorities are looking into the TV rights contract will set alarm bells ringing in FIFA.

In 2005, Blatter signed a contract selling the Caribbean rights for the South Africa 2010 World Cup and Brazil 2014 to the Warner-controlled Caribbean Football Union (CFU) for about 3% of the sum that Warner sold them on for.

Investigations by Press Association Sport have shown that Warner, the disgraced former FIFA vice-president and at that time CFU's president, sub-licensed the rights to his own Cayman Islands-registered company J & D International (JDI).

In 2007, JDI sold on the rights to Jamaica-based cable TV station SportsMax for a value that the broadcaster reported on its own website as being between US$18m and $20m.

Lauber disclosed that FIFA has already sent prosecutors its explanation for the contract.

He said: "We analyse all facts including this explanation of FIFA we received on Sunday evening. We have a lot of facts out of house searches and documents we seized. This specific case we received on Sunday and it will be analysed by us to see if this is really valuable or not."

Mark Pieth, a Swiss professor of criminal law and FIFA's former anti-corruption adviser, said Blatter should face a criminal investigation for alleged selling of such under-valued rights saying there was "prima facie" evidence about the sale which saw Warner make a profit of at least €15m.

Pieth said: "Blatter has to defend himself against a form of embezzlement charges. They have prima facie evidence. That means they have to open an investigation."

Swiss TV programme SRF on Friday published a contract signed by Blatter showing the TV rights for the 2010 World Cup had been sold for $250,000 and the 2014 tournament for $350,000 dollars to the Warner-controlled CFU.

FIFA's said its deal with the CFU included an agreement for a 50% of any profits from sub-contracting the rights - but few if any payments from profit share were ever made by Warner and in July 2011, a month after he resigned from FIFA following bribery allegations, FIFA terminated its contract.