The 22-year-old, who was born in Iraq, winning one cap for the U23 side, came through the ranks at Premier League Tottenham Hotspur, before moving to the Seagulls in October 2010
Kasim made his debut for Brighton in May 2011, starting a League One 1-1 against Notts County.
Last season, he made just one appearance in another 1-1 draw, this time with Town’s Conference rivals Wrexham in the FA Cup.
Hatters boss Paul Buckle said: “Yaser is a strong midfielder and a great prospect whom I first saw as a teenager at Tottenham.
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“Yaser can do a variety of jobs in midfield - he can be a box-to-box man and can also play in a defensive midfield role.
“It is great that we have been able to capture someone of his calibre for six months and I have no doubt that he will prosper with us.”
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