United Nations chief Antonio Guterres spoke to the foreign ministers of Russia and Ukraine on Monday, expressing “serious concern” over the heightened tensions between the countries, his spokesman said.

During the telephone talks, Guterres told Russia’s top diplomat Sergei Lavrov and Ukrainian Foreign Minister Dymtro Kuleba that diplomacy was the only way forward, said spokesman Stephane Dujarric.

“The secretary general expressed to both foreign ministers his serious concern over the heightened tensions around Ukraine,” Dujarric told reporters.

“He welcomed the ongoing diplomatic discussions to defuse those tensions and underline yet again the fact that there is no alternative to diplomacy,” the spokesman added.

Dujarric said Guterres was still convinced that Russia will not invade Ukraine, a position he expressed during a press conference on January 21.

“I dont believe his opinion has changed in any way,” said the spokesman during his daily briefing at the UN headquarters in New York.

The head of the world body was due to attend a monthly lunch Monday with 15 UN Security Council ambassadors at the diplomatic mission of Russia, which currently holds the rotating presidency of the council.

Afterwards, Guterres will make a statement to the media, Dujarric said.

The United Nations has some 1,660 staff in Ukraine including 1,440 Ukrainians and 220 foreigners.

“There are no plans for evacuation or relocation of UN staff” from Ukraine, Dujarric said.

The Security Council is due Thursday to hold an annual meeting on Ukraine and the Minsk agreements, which sought to end war in the eastern Donbas region of Ukraine.