(Reuters) -Following are reactions from foreign governments to the news from Russia, where President Vladimir Putin vowed on Saturday to crush what he called an armed mutiny after rebellious mercenary chief Yevgeny Prigozhin said he had taken control of a southern city.

BRITISH DEFENCE MINISTRY, IN A REGULAR INTELLIGENCE UPDATE

"Over the coming hours, the loyalty of Russia's security forces, and especially the Russian National Guard, will be key to how this crisis plays out. This represents the most significant challenge to the Russian state in recent times."

Britain said (Prigozhin's) Wagner Group forces had crossed from Russian-occupied parts of Ukraine to Russia in at least two locations, and had "almost certainly" occupied key security sites in Rostov-on-Don.

"Further Wagner units are moving north through Voronezh Oblast, almost certainly aiming to get to Moscow," Britain said.

"With very limited evidence of fighting between Wagner and Russian security forces, some have likely remained passive, acquiescing to Wagner."

NATO SPOKESWOMAN OANA LUNGESCU

NATO is "monitoring the situation" in Russia, she said in an email.

ESTONIAN PRIME MINISTER KAJA KALLAS

"Estonia is closely following the development of the situation in Russia and exchanging information with allies. I can assure that there is no direct threat to our country. Border security has been strengthened. I also urge our people not to travel to any part of Russia."

POLISH PRESIDENT ANDRZEJ DUDA, ON TWITTER

"In connection with the situation in Russia, this morning we held consultations with the prime minister and the ministry of defence, as well as with allies.

"The course of events beyond our eastern border is monitored on an ongoing basis."

FRENCH PRESIDENTIAL OFFICE

The Elysee Palace said President Emmanuel Macron is following the situation in Russia closely.

"We stay focused on the support to Ukraine," the Elysee said.

GERMAN GOVERNMENT SPOKESPERSON

"We are monitoring events in Russia closely."

ITALIAN PRIME MINISTER GIORGIA MELONI'S OFFICE

"Prime Minister Meloni is closely following events in Russia, which show that its assault on Ukraine is causing instability within Russia."

GERMAN FOREIGN MINISTRY

The ministry told travellers to avoid the city of Rostov and the surrounding area as well as Moscow city centre until further notice.

"In Moscow, state, especially military facilities, are to be avoided. The city centre should be avoided until further notice. The instructions of Russian security authorities should be followed at all costs," it said in its updated travel advice.

BRITISH FOREIGN MINISTRY STATEMENT

In an update of advice to travellers that continued to advise against all travel to Russia, the ministry said.

"There are reports of military tensions in the Rostov region and a risk of further unrest across the country. Additionally, there is a lack of available flight options to return to the UK."

(Reporting by Reuters bureaus; Compiled by Frances Kerry; Editing by Hugh Lawson)