United Nations, June 22 : UN Secretary-General Antonio Guterres has expressed grave concern about the current tension between Lithuania and Russia over Kaliningrad, said his spokesman. "We are, obviously, following these developments very closely in and around Kaliningrad, including the warnings we have seen of possible escalation, which are very concerning," said Stephane Dujarric, the UN spokesman, on Tuesday. "It's very important for us that all sides deal with their concerns through effective dialogue with appropriate diplomatic channels, in accordance with international law, and to refrain from any statement or from any action that could aggravate the tense situation," he added. Lithuania announced last week that it would ban the rail transit of goods subject to EU sanctions through its territory to the Russian enclave of Kaliningrad, Xinhua news agency reported. The Russian Foreign Ministry on Monday summoned the Lithuanian charge d'affaires and demanded the restrictions be immediately lifted, calling them "provocative" and "openly hostile". The Russian Foreign Ministry on Tuesday summoned the Head of the European Union Delegation to Russia and demanded the restrictions be lifted immediately, saying retaliation would follow if cargo transit was not restored. /IANS