02:26 - Source: CNN
Putin: Don't mess with us, we're nuclear

Story highlights

NEW: European Union leader: More sanctions against Russia to be considered

Ukraine's President says thousands of foreign troops are on Ukrainian soil

President of Ukraine: 'Point of no return' may come if escalation continues

Ukrainian forces bolster defenses around southern port of Mariupol

Mariupol, Ukraine CNN —  

Ukrainian President Petro Poroshenko warned Saturday that his nation’s crisis with Russia has worsened in recent days and is inching closer to a “full-scale war.”

“I think we are very close to the point of no return,” Poroshenko said following an EU summit in Brussels, Belgium. “The point of no return is full-scale war, which already happened in the territory controlled by separatists and where – instead of separatists – there are regular Russian troops.”

Poroshenko said thousands of foreign troops and hundreds of foreign tanks are now on Ukrainian territory.

Russia has repeatedly denied supporting the rebels or sending troops over the border. But the West has rejected Moscow’s denials.

European Council President Herman Van Rompuy, speaking at a meeting in Brussels, said new sanctions are in the works for Russia.

“The European Council says that it stands ready to take further significant steps in the light of the evolution of the situation on the ground and it requests the commission to urgently undertake preparatory work … and present proposals for consideration within a week,” Rompuy said.

As condemnation from the West escalated, Putin was defiant.

Moscow doesn’t want or intend to wade into any “large-scale conflicts,” Putin said, according to state-run ITAR-Tass. A few breaths later, he said Russia is “strengthening our nuclear deterrence forces and our armed forces,” making them more efficient and modernized.

“I want to remind you that Russia is one of the most powerful nuclear nations,” Putin said. “This is a reality, not just words.”

German Chancellor Angela Merkel and U.S. President Barack Obama agreed in a phone call Thursday that they would have to consider tougher action against Russia.

The European Union and the United States have already slapped economic sanctions on targeted Russian individuals and businesses. The union also has sanctioned certain sectors of the Russian economy, prompting Russia to retaliate with its own measures.

Ukrainian port city fortifies defenses

The Ukrainian military worked to fortify the port city of Mariupol after Russian intelligence groups were observed there, said Col. Andriy Lysenko, a spokesman for the Ukrainian National Defense and Security Council.

A CNN team saw Ukrainian forces strengthening defensive positions on the eastern outskirts of the city, reinforcing checkpoints and digging trenches along roads leading toward the Russian border.

Beyond these checkpoints, the team found a small advance detachment of Ukrainian troops on the main road about halfway between Mariupol and Novoazovsk.

The CNN team encountered the first pro-Russian rebel roadblock a short distance outside Novoazovsk, about 12 miles (20 kilometers) from the Russian border, with concrete blocks across the road and a heavy machine gun among the weaponry.

A 12.7 mm heavy machine gun was among the weapons at the roadblock. The fighters would not allow the CNN team to pass through but said they should “come back tomorrow.”

There is a large stretch of territory east of Mariupol, some 15-30 kilometers wide depending on location, that is occupied by neither Ukrainian forces nor pro-Russian fighters.

In the villages between the two “front lines” there are no signs of damage. Some stores are open and there is some civilian traffic on the roads. Long queues have formed at one checkpoint out of Mariupol as people from rural areas try to get in and out of the city.

Months of violence leads to thousands of deaths

Russia annexed Ukraine’s Crimean Peninsula in March, following the ouster of pro-Moscow President Viktor Yanukovych the previous month.

Violence broke out in the eastern Donetsk and Luhansk regions in April, as separatist leaders declared independence from the government in Kiev. Since mid-April, the conflict between the pro-Russia rebels and the Ukrainian military has cost more than 2,500 lives, according to the United Nations.

White House spokesman Josh Earnest said Friday that – whatever the Kremlin says – the reality is Russian troops are inside Ukraine and have fired on Ukrainian military positions.

See the NATO satellite images

In response, Foreign Minister Sergey Lavrov said NATO had previously used “images from computer games” to – in his view – falsely make the case that Russian troops are in Ukraine, and said the “latest accusations are pretty similar.”

CNN’s Tim Lister reported from Mariupol and Laura Smith-Spark wrote and reported in London. CNN’s Lindsay Isaac, Max Foster, Alla Eshchenko, Barbara Starr and Greg Botelho contributed to this report, as did journalist Victoria Butenko in Kiev.