About a thousand Sierra Leoneans who had used the land border to cross from Liberia into their home country to vote were stopped from returning late on Wednesday.
They were stopped after Liberian officials began to suspect they had been joined by other Sierra Leoneans trying to illegally enter the country, immigration authorities told the BBC.
Lemuel Reeves, commissioner of the Liberia Immigration Services, said those blocked from crossing the Mano River Bridge, which runs between the two countries, included women with babies and small children.
Sierra Leonea had asked Liberia to allow its citizens “free passage” so they could take part in the presidential and general elections, according to Mr Reeves.
But he said hundreds of others joined the returning Sierra Leoneans and “tried to force their way to enter Liberia”.
“They don’t have any travel documents, you don’t cross borders just like that, they want to come into this country freely, it is our job to screen them,” he said.
Mr Reeves said they had allowed in all those with travel documents.
However, an eyewitness told the BBC between 20 and 50 buses were waiting on the Liberian side of the border to transport the Sierra Leoneans to Monrovia but they were still being held at nightfall.
Refugees from Liberia and Sierra Leone ended up in their neighbouring countries during their respective civil wars, but years later, there are still thousands who are still living in their neighbouring country. But on this visit the minister also brought President Emmerson Mnangnagwa a special message from Russia’s President Vladmir Putin: a promise to help stablilise the country, politically and economically.
Mr Lavrov has now left for Ethiopia, where he is expected to meet African Union representatives.