The International Criminal Court on Tuesday excused Kenya's Deputy President William Ruto from attending parts of his crimes against humanity trial in September because of demands placed on him in Nairobi.

The Hague-based court's trial chamber "conditionally granted... the request of William Ruto to be excused from being physically present continuously throughout the trial," scheduled from September 10, the ICC said in a statement.

Ruto, 46, faces three counts of crimes against humanity for his role in deadly violence that erupted in Kenya after elections in late 2007 which claimed some 1,100 lives and displaced 600,000 people.

Judges earlier this month postponed the trial, with which Ruto, sworn in as the east African country's deputy leader in April, pledged his full cooperation.

The judges also recommended that part or all of the high-profile trial may be held in Kenya or Tanzania.

"The Chamber stressed that permission granted to Mr Ruto to not be continuously present was strictly for the purposes of accommodating the demanding functions of his office as deputy head of state of Kenya," the ICC said.

"The resulting absence from the trial must therefore always be seen to be directed towards performance of those duties of state," it added.

Ruto remains under the court's "judicial control" during the entire hearing and the ICC, the world's only permanent independent court to try the worst crimes, warned any violation could result in the agreement being nixed and the issuing of an arrest warrant.

Ruto must also be present at the opening and closing statements of all parties and participants in the case; when victims are present at the trial; when a judgement is delivered and if needed, a sentence is handed down.

Ruto is to go on trial with his co-accused, radio boss Joshua arap Sang.

What began as post-election riots in 2007 quickly turned into ethnic killings and reprisal attacks, plunging the country into its worst wave of unrest since independence from Britain in 1963.

The ICC in January 2012 confirmed crimes against humanity charges against four senior Kenyans including Ruto, Sang and Kenya's newly elected President Uhuru Kenyatta.

Charges against the fourth accused, civil servant Francis Muthaura, have since been dropped.

Judges in early March postponed Kenyatta's own trial until July 9, when he is expected to become the first-ever serving head of state to face the ICC's judges.