Member states of the International Criminal Court (ICC) have agreed to amend its rules to let some defendants give evidence via video link.
The change is likely to affect the trial of Kenyan President Uhuru Kenyatta, due to begin in February.
His legal team had argued he should be able to remain in Kenya so he could continue governing the country.
He denies charges of organising ethnic violence after the 2007 election in which some 1,200 people died.
Mr Kenyatta's deputy, William Ruto, is currently on trial facing the same charges.
The head of the ICC's oversight body, Tina Intelmann from Estonia, told the BBC that the court recognised that a president has national duties to discharge.
She said requests to appear by video-link would be assessed on a case-by-case basis by the court.
"First of all the chamber has to look that the rights of the accused are fully ensured, that it's actually not only the obligation of the accused to be present, but also the right of the accused to be present."
However, Kenyan officials rejected the development - they want sitting heads of state to be immune from prosecution altogether.
"We want exclusion, the exclusion of heads of state from the process," said Kenya's ICC ambassador Macharia Kamau.
But human rights campaigners expressed dismay at the ICC's move.
Elizabeth Evenson of Human Rights Watch said the decision "risks putting in place a two-tiered justice and undermining perceptions of the court's legitimacy".
Mr Kenyatta will become the first serving head of state to go on trial at the ICC.
William Ruto's trial began in September but was adjourned for a week to let him return home to deal with the aftermath of the Westgate shopping centre attack in which 67 people died.
The court ruled that he must attend most of his trial - and be excused only on a "case-by-case" basis.
The ongoing debate regarding Mr Kenyatta's impending trial has undergone several twists and turns.
Judges had ruled in October that he only needed to be present at the Hague for key parts of the case.
But on Tuesday the ICC reversed the ruling, saying he should, "as a general rule", be present in court.
The African Union has been calling for the trial to be delayed.
Earlier this month, the UN Security Council rejected a request from African states to suspend the ICC trial of both President Kenyatta and Mr Ruto.