EU leaders are set to meet in Brussels to discuss firmer action against Russia over the Ukraine crisis.
Ukraine President Petro Poroshenko is also due to attend.
The meeting comes after NATO said Russia had sent well over 1,000 troops and heavy weaponry into Ukraine.
Russia has rejected accusations that it invaded Ukraine.
On August 29, several EU foreign ministers voiced support for fresh sanctions.
These would be in addition to measures already imposed against dozens of Russian officials, several companies and the country's financial industry, leveled by the United States and EU earlier this summer.
Polish Foreign Minister Radoslaw Sikorski said Russian "aggression" had created the most serious security crisis in Europe for decades, and German Foreign Minister Frank-Walter Steinmeier warned of a possible broader conflict between Russia and Ukraine.
Swedish Foreign Minister Carl Bildt said on August 29 that "we have to be aware of what we are facing: We are now in the midst of the second Russian invasion of Ukraine within a year."
In Bucharest on August 29, Romanian President Traian Basescu said that in addition to new sanctions, NATO members should arm Ukraine's army.
Earlier, Ukrainian Prime Minister Arseniy Yatsenyuk called for full membership in NATO, scrapping the country's nonaligned status.
NATO Secretary-General Anders Fogh Rasmussen said he respected Ukraine's right to seek alliances.
Meanwhile, Russian President Vladimir Putin compared Kyiv's drive to regain control of its rebellious eastern cities to the Nazi invasion of the Soviet Union in World War II.
Pro-Russia separatists held firm control on August 29 of the strategic coastal town of Novoazovsk, a day after Ukraine claimed tanks and armored vehicles had invaded from Russia.
A spokesman for the rebels in Novoazovsk, who identified himself only as Aleksandr, said their plan was to try to eventually push westward to the major port city of Mariupol, about 35 kilometers away.
There are fears the rebels' eventual aim is to establish a land bridge between Russia and the Russia-annexed Crimea peninsula further to the west.
With reporting by AP and Reuters