Ukraine crisis: OSCE 'must double' ceasefire monitors
Russia and Germany have called on the OSCE to double the number of observers monitoring a truce in eastern Ukraine to 1,000.
Russian Foreign Minister Sergei Lavrov and his German counterpart Franck-Walter Steinmeier urged the OSCE to "ramp up" its mission.
The group has said it has experienced problems gaining access to key areas.
Meanwhile, Ukrainian government sources told the BBC they believed Russian troops were still entering the country.
According to some claims, there could be at least 18,000 involved.
Last month's ceasefire agreement reached in Minsk required all foreign troops to leave the region.
Organization for Security and Co-operation in Europe (OSCE) Secretary General Lamberto Zannier said his assessment was that the truce was holding, but he acknowledged "violations".
He told Reuters that the group was struggling to roll out its current mission, aimed at ensuring the removal of weapons and the implementation of the ceasefire.
"My main problem in this moment is not the numbers, it's the access," Mr Zannier said.
"If they had more access, I could get more out of them. That is really my challenge."
The EU's policy chief Federica Mogherini, agreed the OSCE's presence on the ground should be increased, but said it needed "guaranteed access".
Speaking after a meeting of foreign ministers in Riga she said there were plans to provide monitors with satellite equipment to observe areas "it is not possible to reach physically".
Analysis: Gavin Lee, BBC News, Riga
The two day talks here in Riga are dominated by the fragile ceasefire in Ukraine and the intensifying civil war in Libya.
But Latvian and Lithuanian ministers tell me they're using the summit to raise the issue of the perceived threat of Russia's "information war".
They claim anti-EU television and media propaganda is targeting the minority Russian speakers in the Baltic states.
The Secretary of State for the Latvian Defence Ministry, Janis Sarts, believes Russian propaganda is directly affecting some of the country's 500,000 Russian speakers, a quarter of its population.
He spoke of a "spell of propaganda" he feels is being used to destabilise the situation, alongside alleged military intimidation.
On Monday, the leaders of Russia, Germany and France agreed to Ukraine's proposal to ask the OSCE to help with ensuring the ceasefire was held.
Both Ukraine and the pro-Russian rebels say they are withdrawing heavy weapons from the combat zone. But there have been reports of fighting.
Earlier, senior figures in the US Congress called for Washington to send lethal defence weapons to Ukraine.
US President Barack Obama is said to be studying the option, but this would put him at odds with some European leaders, notably German Chancellor Angela Merkel.
US Deputy Secretary of State Antony Blinken told German radio on Friday that if aggression from pro-Russian separatists continued, the need to help the Kiev authorities "protect themselves" would only increase.
"We also know that if we were to supply more defence technology, Russia could easily counter that by providing two, three or four times what we do," he told DLF.
The Ukraine crisis is set to dominate the two-day talks in Riga.
Ms Mogherini admitted the ceasefire agreed in Minsk last month was "not perfect", but described the overall outlook as "positive".
She said the European Union was "doing enough'' and insisted that the implementation of the peace deal was "the way to go forward".
Latvia and its Baltic neighbours Estonia and Lithuania have voiced concern about what they see as Russia's increasingly aggressive attitude.
They fear Nato and the EU have moved too slowly to counter Russia's actions.
Nato has increased its military presence in the Baltic states, with several military drills and training exercises in Lithuania in recent weeks.
Correspondents say it is a deliberate show of force and an act of unity against an alleged threat from Russia to the former Soviet states.
On Thursday Russia announced large-scale military exercises in the annexed Crimea, as well as breakaway regions of Georgia.
At least 6,000 people are believed to have been killed since the conflict in Ukraine's eastern Donetsk and Luhansk regions erupted last April, a month after Russia annexed Ukraine's southern Crimea peninsula.