The first United Nations observers assigned to monitor the Persian Gulf war cease-fire have arrived in Baghdad and Tehran.

A five-member U.N. team arrived in Baghdad on Tuesday night, a Western diplomat said on Wednesday. The Iranian news agency IRNA reported a similar five-man group had arrived in Tehran on Wednesday morning.IRNA, received in Nicosia, said five members of the United Nations Iran-Iraq Military Observer Group had arrived to prepare the ground for the implementation of the cease-fire scheduled to take effect Aug. 20.

"The team will hold talks with Iranian political and military officials to prepare the ground for the arrival of the U.N. observer force," IRNA said. "The group will be stationed in southern and western areas of the country to supervise military movements until establishment of the cease-fire," the agency added.

IRNA repeated war supremo Akbar Hashemi Rafsanjani's statement made on Tuesday calling on Iranian forces throughout the war fronts to refrain from military action while remaining alert to "respond to enemy mischief."

Canada is providing 370 military personnel for the 24-nation peacekeeping force. The other nations are Argentina, Australia, Austria, Bangladesh, Denmark, Finland, Ghana, Hungary, India, Indonesia, Ireland, Italy, Kenya, Malaysia, New Zealand, Nigeria, Norway, Poland, Senegal, Sweden, Turkey, Yugoslavia and Zambia.

Each country will provide approximately 10 to 15 officers for the U.N. observer group. Canadian officials said on Tuesday that its group of soldiers will be responsible for all communications requirements.

The unit, assigned to the entire 750-mile border between the two countries, is in addition to 15 officers assigned to headquarters and observer positions, External Affairs minister Joe Clark said.

U.N. Secretary General Javier Perez de Cuel-lar has yet to name the group's commander.

He estimated the cost of the operation would be $74 million for an initial six-month period.

In Washington, White House spokesman Marlin Fitzwater on Wednesday said Persian Gulf nations would be urged to donate a substantial portion of the peacekeeping effort's cost.

"We'll be giving the same message to other countries like Japan and others who have an interest in the gulf," Fitzwater said.

Japan, which imports nearly all its oil from the gulf region, already has donated $20 million this year to U.N. peacekeeping efforts, earmarking half of the amount for the Iran-Iraq peace effort.