Poroshenko, who met German Chancellor Angela Merkel in Berlin on Monday, said Russia had implemented "not one single point" of the Minsk accord, which includes a ceasefire between Ukrainian troops and pro-Russian rebels in eastern Ukraine.
Russia was building up its military presence on the border with Ukraine, he said.
"The danger of an open war is greater than last year," Poroshenko told Bild, in an interview published in its Wednesday edition.
"Russia is investing a great deal in war preparations."
Merkel pressed Putin by phone on Tuesday to use his influence to ensure that a ceasefire is upheld in Ukraine and that monitors from the OSCE European security organization are granted free access to conflict areas, her spokesman said.
Berlin is growing increasingly suspicious that Russia is trying to stir up trouble in Germany to try to weaken Merkel, who has taken a tough line on a crisis that was triggered when Russia annexed Crimea in March 2014.
German concerns about Moscow grew last month after Russian Foreign Minister Sergei Lavrov accused the German authorities of "sweeping problems under the rug" over an alleged rape case involving a German-Russian girl.
The case of the 13-year-old, named only as Lisa F., caused controversy after she told police that she had been kidnapped in east Berlin last month by migrants who raped her while she was held for 30 hours.
The Berlin public prosecutor's office has since said a medical examination found she was not raped.
When asked if Russia had used the case to try to stir up tensions around immigration, Dmitry Peskov, a spokesman for the Kremlin, told reporters on Wednesday:
"We cannot agree with such accusations."
"On the contrary, we were keen that our position be understood, we were talking about a citizen of the Russian Federation," he added.
"Any country expresses its concerns (in such cases). It would be wrong to look for any hidden agenda."
Source: Google News