The United Nations on Thursday called for "maximum restraint" from all parties amid heightened tensions between Iran and the United States and in the Gulf region.

"We are very concerned about the volatility of the situation. We call on everyone to exercise maximum restraint, prevent any escalation of and heightening of tensions," Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres, told reporters.

"The situation ... is already fairly volatile and we are concerned by the rhetoric that we have been hearing," he told a regular press briefing.

Guterres is following the situation very closely and contacts have been made, said Dujarric.

"We are following the situation. Our message, and the secretary-general's general message, is one of restraint, both in terms of actions and in terms of rhetoric. These are situations where actions and rhetoric can be misinterpreted and can lead to catastrophic actions. It's very, very important that we see restraint both in terms of the rhetoric and in terms of the action."

He said the secretary-general's good offices remain available at request. "But through the contacts that we have, we remain very much involved and are following the situation very closely."

The United States has ramped up pressure on Iran, by designating Iran's Islamic Revolution Guards Corps as a terror group, imposing a total ban on Iranian oil exports, and building up its military presence in the Gulf.