Ukraine's president yesterday announced a partial call-up of reservists for training amid tensions with Russia, saying the country needs to beef up its defenses to counter the threat of a Russian invasion.

The Kremlin called absurd a Ukrainian accusation it has designs on the Ukrainian ports of Mariupol and Berdyansk in order to create a land corridor between Russian-annexed Crimea and eastern Ukraine controlled by pro-Russian separatists. "It's an absurd statement," Kremlin spokesman Dmitry Peskov said. "It's another attempt to generate tension."

Relations between the two neighbors have been strained further following a Nov. 25 incident in which the Russian coast guard fired upon and seized three Ukrainian naval vessels and their crews off the Crimean Peninsula that Russia annexed from Ukraine.

Ukrainian President Petro Poroshenko responded by introducing martial law for 30 days in much of Ukraine. For the duration of martial law, Ukrainian authorities barred entry to all Russian males aged 16 to 60 in a move the Ukrainian leader said was needed to prevent Russia from further destabilizing the country.

Poroshenko said yesterday that some reservists will be summoned for training as part of martial law. He also said that some military units will be redeployed to strengthen the nation's defenses. "Ukraine is taking its own steps in response to the threat of a large-scale Russian invasion," the Ukrainian leader said.

Over the weekend, Poroshenko said that Russia has deployed a large number of troops along its border with Ukraine and alleged that the Kremlin intends to push inland into Ukraine. Ukraine also accused Russia of blockading its ports on the Sea of Azov. Peskov rejected Kiev's claim that Russia was blocking traffic to and from Ukrainian ports on the Sea of Azov, saying that navigation has continued normally except for occasional breaks because of bad weather.

Russia and Ukraine traded blame for the confrontation that raised the specter of a full-blown conflict between the neighbors. Ukraine said its vessels were heading to the Sea of Azov in line with international maritime rules, while Russia charged that they had failed to obtain permission to pass through the narrow Kerch Strait that is spanned by a bridge that Russia completed this year. The incident sharply escalated tensions that have been growing between the two countries since Moscow annexed Crimea from Ukraine in 2014.