Close to 100 women have fallen victim to "rampant" sexual attacks in Cairo's Tahrir Square during four days of protests against Egypt's Islamist President Mohammed Morsi, Human Rights Watch said on Wednesday.

"Mobs sexually assaulted and in some cases raped at least 91 women in Tahrir Square... amid a climate of impunity," HRW, which is based in New York, said in a statement.

The Gulf state of Kuwait on Wednesday urged its citizens in Egypt to leave "at the earliest" and warned against travel to the country after President Mohammed Morsi rejected an ultimatum by the army, amid mass protests and deadly clashes.

"All Kuwaitis present in Egypt must leave at the earliest due to the developments and events in various parts of the country," the official KUNA news agency cited ambassador Rasheed al-Hamad as saying.

Unidentified gunmen killed 16 people and wounded 200 others when they opened fire at a Cairo rally supporting embattled Egyptian President Mohammed Morsi, health ministry officials said Wednesday.

"Sixteen people have been killed and 200 wounded in an attack on a demonstration supporting President Morsi next to Cairo University," state television reported, citing the ministry.

Islamist President Mohamed Morsi told Egyptians on Tuesday that he had been freely elected little more than a year ago and that he intended to continue to carry out his duties despite mass protests demanding his resignation.

"The people chose me in free and fair elections," Morsi said in a televised address to the nation, adding that he would "continue to shoulder his responsibilities" as Egypt struggles with the legacy of decades of authoritarian rule.

Egyptian President Mohamed Morsi must listen to the voices of the people to resolve a damaging political crisis which could lead to military intervention, a U.S. official said Tuesday.

Morsi, an Islamist leader who became the country's first democratically elected president, was Tuesday locked in talks with the army chief Abdel Fattah al-Sisi, amid mounting calls from the opposition that he should step down a year after his election.

Egypt's Islamist leader Mohamed Morsi must "hear" popular demands, French Foreign Minister Laurent Fabius said Tuesday, after the defiant president snubbed an ultimatum to step down.

"When there is such a mass of problems and a such a mass of people expressing what is not than just unease but censure and distress, the Egyptian government must listen to the people... President Morsi must hear what is taking place," he said on the i-Tele network.

A top Muslim Brotherhood leader urged Egyptians to stand ready to sacrifice their lives to prevent a coup, after the army gave Islamist President Mohamed Morsi and his opponents until Wednesday to resolve their differences or face intervention.

"Seeking martyrdom to prevent this coup is what we can offer to the previous martyrs of the revolution," Mohamed al-Beltagui said in a statement on Tuesday.

German Foreign Minister Guido Westerwelle expressed grave concern Tuesday about Egypt's political crisis and urged all sides not to squander the hopes of the democratic revolution.

"I am deeply concerned and I do not want to hide it," he told reporters.

U.N. Secretary General Ban Ki-moon on Tuesday expressed concern about sexual violence used against female protesters in Egypt, where millions have taken to the streets to demand the ouster of President Mohamed Morsi.

"I really hope that while addressing all this current crisis in a peaceful manner, they (Egyptians) should pay more attention to the female demonstrators since we have seen many sexual assault cases over the course of the demonstrations," he told reporters in Reykjavik.

Opponents of Egypt's Mohamed Morsi poured onto the streets of Cairo on Tuesday to press their demand that he step down after the Islamist president snubbed an ultimatum from the army to agree to the "people's demands" or face an imposed solution.

Morsi and army chief Abdel Fattah al-Sisi have been locked in talks all day to "discuss the current crisis," a military source said, as clashes in Cairo between opponents and supporters of the president left seven people dead.