UNITED NATIONS -- The UN Secretary-General Ban Ki-moon Thursday night called on all sides in Yemen "to exercise maximum restraint", after both the country's president and prime minister submitted their resignation.

Ban is "seriously concerned" about developments in Yemen, where President Abd Rabbo Mansour Hadi and Prime Minister Khaled Bahah submitted their resignation on Thursday, said a statement from Ban's spokesperson.

"In these uncertain times in the country, the secretary-general calls on all sides to exercise maximum restraint and maintain peace and stability," it said.

Hadi submitted his resignation to the parliament amid standoff with the Shiite Houthi group who control the capital. Shortly before that, Prime Minister Bahah offered to resign to Hadi.

The government signed on Wednesday a peace deal with the Houthi group which seized the presidential palace during clashes with presidential guards since Monday.

Ban urged all sides to remain fully engaged with his Special Adviser on Yemen Jamal Benomar, who is in the capital Sanaa. "Benomar is consulting closely with all sides to help find a way forward from the current crisis," said the statement.