German Chancellor Angela Merkel met with Ukrainian President Petro Poroshenko in Kiev Saturday to show support for the country in its four-month-old conflict with pro-Russian separatists and to push for peace between Ukraine and Russia, Reuters reported. Merkel said better border control and a cease-fire are necessary before peace can be achieved.

Poroshenko will meet with Russian President Vladimir Putin Tuesday. “The Ukrainian side and our European partners will do everything possible to bring about peace -- but not at the price of sovereignty, territorial integrity and the independence of Ukraine,” Poroshenko said Saturday. Merkel suggested the creation of a pact between the two countries and the Organization for Security and Cooperation in Europe, OSCE, to observe the border, Reuters said.

“There must be two sides to be successful,” Merkel said. “You cannot achieve peace on your own. I hope the talks with Russia will lead to success.”

Ukrainian forces have gained traction in the eastern portion of the country, recently taking control of a police center within the city limits of Luhansk and through heavy fighting in Donetsk, the pro-Russian separatist stronghold. Reuters speculated heavy clashes overnight could have been related to Ukraine’s desire to secure an important military victory ahead of the nation’s Independence Day Sunday.

Another bone of contention is the Russian humanitarian convoy that entered eastern Ukraine without the country’s permission. NATO condemned the move Friday, saying, “This is a blatant breach of Russia’s international commitments, including those made recently in Berlin and Geneva, and a further violation of Ukraine’s sovereignty by Russia.”

Saturday, OSCE reported the convoy left Ukraine and returned to Russia. “The OSCE Observer Mission (OM) concludes that all 227 vehicles of the aid convoy, which had crossed the Donetsk BCP towards Ukraine on 22 August, have returned to the Russian Federation (RF),” OSCE said.