International Criminal Court chief prosecutor Fatou Bensouda offered Tuesday to help prosecute those behind the deadly attack on Nairobi's Westgate shopping mall, a statement said.

Bensouda expressed "her deep sympathy to the victims of the appalling attack", which "may constitute a crime" under the ICC's founding Rome Statute, to which Kenya is a party.

"With full respect for the primacy of jurisdiction of the Republic of Kenya, the prosecutor stands ready to work with the international community and the government of Kenya to ensure that those responsible for these crimes are brought to justice," Bensouda said.

Islamist Shebab fighters claim still to be holding hostages inside Nairobi's Westgate mall, as they continued to battle special forces on the fourth day of a deadly siege.

At least 62 shoppers and staff have been killed and close to 200 wounded in the siege, but concerns are high that the toll may yet rise.

Judges at the Hague-based ICC on Monday adjourned for a week Kenyan Vice President William Ruto's crimes against humanity trial for violence following a disputed 2007 election so he could deal with the hostage crisis.

The ICC is the world's only independent, permanent tribunal for war crimes, genocide and crimes against humanity.

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