Russia has left the door open for further dialogue with the United States in the stand-off over Ukraine, but said rejection of its concern about Nato's expansion eastwards left "little cause for optimism".
Moscow had sought a veto over Ukraine's potential membership of the Nato military alliance. But the US and Nato have formally rejected this as unacceptable, saying that all countries were free to seek membership.
Tensions have escalated in recent weeks as Russia has mobilised more than 100,000 troops on its border with Ukraine, stirring fears that President Vladimir Putin is considering an invasion.
Russian foreign minister Sergei Lavrov said that Moscow's main concern, the potential for Ukraine to join Nato, had not been addressed by the US or Nato in their response to proposals from Moscow. But he added that there was still hope for "serious" dialogue on "secondary" issues.
The US has said it hopes that Russia would study what Washington had offered and return to discussions, but warned of “severe” action if diplomacy fails.
"We are unified, unified in our preference for diplomacy. But we are also unified in our resolve that if Moscow rejects our offer of dialogue, the costs must be swift and severe," said high-ranking US diplomat Victoria Nuland.
China has signalled its support for Russia, saying that Moscow had "reasonable" security concerns that should be "taken seriously" by the US and its allies.
The country's foreign minister, Wang Yi, hinted at Chinese support for Russia's opposition to Nato's expansion into eastern Europe. Mr Wang told US secretary of state Antony Blinken in a call that "regional security cannot be guaranteed by strengthening or even expanding military blocs".
Meanwhile, Russian ambassador to Ireland Yuriy Filatov is set to appear before the Oireachtas foreign affairs committee to face questions on the crisis, Russia's planned naval exercises off the Irish coast and a tweet featuring him and Defence Forces chief of staff Lieut Gen Seán Clancy.
Committee chairman Charlie Flanagan, a former minister for foreign affairs, said he wanted to ask Mr Filatov what was meant in the tweet by the words “prospects of contacts between armed forces” of Russia and Ireland.
Sources said the hope was that Mr Filatov would agree to appear at the committee next week.
There was controversy yesterday over remarks by Minister for Defence Simon Coveney regarding the meeting, which he told a Fine Gael parliamentary party meeting had taken him by surprise. However, the Minister told the Dáil he had "no reservations or questions" about Lieut Gen Clancy's actions.
The Defence Forces said that the meeting was arranged following a request from the Russian embassy.
Irish fishing groups said they were given assurances by the Russian ambassador that their fishing grounds would not be affected by the Kremlin’s naval drills off the coast next week.
Representatives of two fishing industry groups met Mr Filatov amid concerns over the drills in international waters 240km off the coast of west Cork but in the State's exclusive economic zone.
Up to 60 Irish trawlers are planning to fish in the area from next week in an area close to where the military exercises take place over five days from next Thursday.
The meeting at the embassy took place after the Department of Transport issued a marine notice to all seafarers warning about the “serious safety risks” in the operational area of the drills given the Russian navy’s planned use of artillery and the launching of rockets.
The fishing industry is concerned that the safety notice could invalidate insurance on fishing vessels which plan to start fishing in the area from next week.