"We have asked the UNHCR to relocate the refugees in three months" or "we shall relocate them ourselves", a government statement quoted Vice President William Ruto as saying in a speech Saturday.
The UNHCR said yesterday it had not received the Kenyan request but added that refugees cannot be forcibly repatriated.
Shebab insurgents from Somalia claimed responsibility for the April 2 attack on the university in the east of the country which left nearly 150 people dead.
UNHCR spokesman Emmanuel Nyabera told AFP in Nairobi: "We have not received any formal communication or formal request from the Kenyan government along this line."
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"Kenya has an international obligation to protect the refugees and that includes no forceful repatriation to the country of origin."
Somali refugees in Kenya number around 450,000, most of them at Dadaab, the world's largest refugee camp, the UNHCR said.
The camp opened in 1991 after the collapse of Somalia's hardline Siad Barre regime when the country plunged into chaos.
"Instead of making refugees scapegoats, Kenya -- which is legally obliged to protect them until they can go home safely -- should find and prosecute those responsible for the Garissa massacre," said Leslie Lefkow, the rights group's Africa deputy director.
The Kenyan government had already sought the closure of Dadaab after the September 2013 Shebab attack on the Westgate shopping mall in Nairobi that left at least 67 people dead, saying the camp was a breeding ground for Islamist militants.
In November that year, Kenya, Somalia and the UNHCR signed a joint deal to back the voluntary repatriation of Somalis.
Authorities have detained five Kenyans and a Tanzanian suspected of connections to the university massacre.