Armed Russian and Ukrainian soldiers stood face to face Sunday, eyeing each other across a locked gate at a military installation in Crimea, as residents and an alarmed West asked: What are Moscow’s intentions in Ukraine?

Ukraine’s new prime minister said the bold and provocative Russian troop movements in Crimea in recent days amounted to a “declaration of war to my country.” Ukrainian officials sounded a mobilization order Sunday for army reservists to report for duty immediately.

[Read: Why the situation in Crimea is different from the Georgia-Russia crisis in 2008]

Western officials, including Secretary of State John F. Kerry, were unequivocal in their denunciations of Russia’s intervention in Ukraine. Kerry warned that “the people of Ukraine will not sit still for this. They know how to fight.”

He and European foreign affairs leaders promised Sunday that there would be a strong response to Russia’s decision to “invade” Ukraine, as Kerry put it in an interview on ABC’s “This Week.”

Russian President Vladimir Putin was silent Sunday.

In Kiev, Ukraine’s interim prime minister, Arseniy Yatsen­yuk, said in an emotional plea at a news conference, “We are on the brink of disaster.”

Yatsenyuk, part of a new government that took power after pro-Russian President Viktor Yanukovych was tossed out of office just over a week ago, said armed conflict was a real possibility.

“If President Putin wants to be the president who started a war between two neighboring and friendly countries, Ukraine and Russia, he has reached that target within a few inches,” Yatsenyuk said in English.

Ukrainian leaders worried that Russia was looking for any provocation on their part to justify an attack.

By late Sunday, no shots had been fired in Crimea, a region of eastern Ukraine where Russian culture and influence have historically been strong.

Reports of trenches

But at the narrow land crossing between Crimea and the rest of Ukraine, Russian soldiers are digging trenches, according to a BBC report.

On Monday morning, the Associated Press reported that pro-Russian troops took control of a ferry terminal in the Ukranian city of Kerch, on the eastern tip of Crimera. The terminal serves as a departure point for many ships heading to Russia.

Soldiers thought to belong to Russian units, without insignia or markings, moved unimpeded into positions across the Crimean Peninsula. Over a three-day period, they have surrounded military and civilian installations. Convoys of Russian troop trucks were spotted on highways. A Russian flag flew over the Crimean parliament.

At the Ukrainian military base at Perevalnoe in Crimea, Ukrainian soldiers stood guard while soldiers whom locals described as Russian commandos milled around outside the walls. The Ukrainians refused to surrender their weapons or step aside. A commander of the Ukrainian troops spoke with the men surrounding his base, then went back inside.

Civilians in a pro-Russia crowd outside the base called to the Ukrainian soldiers, “Boys, don’t be afraid, we will protect you!” Others urged them to open the gates and let the Russians in. A Russian Orthodox priest arrived and blessed the Russians and Ukrainians.

“Now we feel safe and patriotic that the Russian soldiers are here for us,” said a man from a nearby village who gave his name as Vladi­mir.

Asked about the Ukrainian soldiers inside the base, Vladimir said: “They should go home. They’re not going to fight. It’s over.”

The loyalties — and the command and control — of the Ukrainian military in Crimea are unknown.

Russian media said Ukrainian troops were not putting up any resistance. Ukraine’s new interior minister, Arsen Avakov, denied reports of mass resignations from the Ukrainian army in Crimea.

But the new head of the Ukrain­ian navy, Rear Adm. Denys Berezovsky, appeared in a video Sunday swearing his allegiance to the “people of Crimea,” as the new pro-Russia prime minister of Crimea stood at his elbow.

Officials in Kiev labeled it a defection and said the admiral would be investigated for treason. They assured citizens that the 10 vessels in the navy’s fleet in nearby Sevastopol remained loyal to Ukraine and have not surrendered their weapons.

In Simferopol, the Ukrainian border guard reported that civilians and Russian soldiers broke down the doors at their base and destroyed work stations and communications equipment but that the border guardsmen did not give up their weapons, according to the Kyiv Post.

Normal life elsewhere

Life in cities and villages went on peacefully. Regional airports were scheduled to open. In pro-Russia Sevastopol, where Russia’s Black Sea Fleet is berthed, citizens had their photos taken beside Russian commandos.

There were rallies in Russia and Ukraine, for and against Russian intervention.

One of richest men in Ukraine, business mogul Rinat Akhmetov, issued a statement denouncing violence and calling for unity, saying: “Today the economy is a real political power. Our objective is to ensure the safety of people and their families and secure stable operations of companies in the country.”

In Dnepropetrovsk, a mostly Russian-speaking city southeast of Kiev, a rally described by local reporters as the largest in years drew an estimated 10,000 people who shouted “Down with Putin!” A similar rally was held in Odessa, Ukraine’s third-largest city. In Luhansk, meanwhile, the city council said it refused to recognize the authority of the new leaders in Kiev, according to the news Web site

In Kharkiv, a hotbed of pro-Russian activists in eastern Ukraine, a few thousand protesters joined a rally Sunday to denounce the Russian move into Crimea.

Police watched from a distance as the demonstrators waved banners saying “Putin get out of Ukraine” and “No to War” and gathered around a statue of 19th-century revolutionary Ukrainian poet Taras Shevchenko.

“Russia is attempting to occupy Ukraine. They won’t win without a fight,” said Maria Shaposhnikova, a university teacher in Kharkiv. “The majority of people want to live in an independent Ukraine.”

In Moscow, police detained about 260 people protesting the Crimea intervention Sunday. Many were put in police vans outside the Defense Ministry, and more than 100 were detained several blocks away at a plaza next to Red Square. The protesters were seemingly detained at random. One man was holding a blank sheet of paper. Another man, who identified himself as a journalist, was picked up as he talked to two women.

Moscow authorities, however, gave permission for a march in favor of the invasion of Crimea and shut off a central boulevard to make way for it.

The protest camp in Kiev’s ­Independence Square, where the Ukrainian uprising began, swelled Sunday as tens of thousands of people turned out to demonstrate against the Russian actions. The camp was established in November after Yanu­kovych abruptly dropped a pending trade deal with the European Union and turned to Russia instead.

Russian television reported that hundreds of thousands of Ukrainians have fled to Russia in recent days, but reports from border crossings suggested that was not true. Video taken at one crossing Sunday showed little activity.

The main Russian television station said it would cancel its broadcast of the Academy Awards because of the tensions with the United States over Ukraine.

Englund reported from Kiev. Kathy Lally in Moscow and Isabel Gorst in Kharkiv contributed to this report.