Both Putin and Merkel voiced concern over the rising tensions in the southeast of Ukraine, the Kremlin said in a statement.

"Vladimir Putin drew attention to the provocative actions of Kiev, which has recently purposefully escalated the situation on the line of contact. The need for the Kiev authorities to strictly implement the previously reached agreements was stressed, first of all, to establish a direct dialogue with Donetsk and Luhansk and to legally formalize the special status of Donbass," it said.

The parties to the conflict were called upon to exercise restraint and intensify the negotiation process to fully implement the 2015 Minsk Agreement as a non-alternative basis for a settlement, it said.

A statement from Merkel’s office has underlined concerns over a large Russian military build-up on the Ukrainian border.

“The chancellor has called for a reduction of these troop reinforcements in order to de-escalate the situation,” Ulrike Demmer, the deputy government spokeswoman, said in a statement.

The two leaders reaffirmed their commitment to further close coordination of efforts between Russia and Germany, including in the Normandy format -- Germany, France, Russia, and Ukraine -- through political advisers and the foreign ministries.

Putin and Merkel also spoke about the humanitarian situation in Syria, welcomed the establishment of state institutions for the transition period in Libya, and stressed the necessity to ensure stability in Bosnia and Herzegovina.

"In connection with the interest shown by the Federal Chancellor, the situation with [Russian opposition figure] A. [Alexey] Navalny was touched upon. At the initiative of Vladimir Putin, some issues related to the activities of foreign media and non-governmental organizations in both countries were considered," the statement noted.

In 2014, Navalny was convicted of fraud and embezzlement, but his two-and-a-half-year sentence was suspended and replaced with six-year probation, required to report to police twice a month. He was arrested in the Russian capital upon his return in January from Germany, where he had received treatment after alleged poisoning by Russian agents last year.

Russia-Ukraine tensions rise

In his speech to the parliament on March 30, Ukrainian Chief of General Staff Ruslan Homchak said the Russian Armed Forces were sending troops near the Ukrainian border on the plea of military exercises.

In response, Kremlin spokesman Dmitriy Peskov said Russia is moving its armed forces within its territory at its discretion and that it does not pose a threat to anyone.

Ukraine has been plagued by conflict in its eastern regions since March 2014, following Russia’s illegal annexation of Crimea.

Fighting between Ukrainian government forces and pro-Russian separatists in eastern Ukraine has seen more than 13,000 people killed, according to the UN.