Pope Francis expressed his sorrow Tuesday over the deaths of dozens of migrants near the border between the United States and Mexico, and at the border between Spain and Morocco.

"I sorrowfully heard the news of the tragedy of the migrants in Texas and Melilla," he said on Twitter.

"Let us pray together for these brothers and sisters who died following their hope of a better life; and for ourselves, may the Lord might open our hearts so these misfortunes never happen again," Francis said.

At least 46 migrants were found dead Monday in and around a large trailer truck abandoned on the outskirts of the Texas city San Antonio.

The grim discovery marked one of the worst disasters involving migrants in the United States in recent years -- and came five years after a similar deadly incident in the same central Texas city, a few hour's drive from the Mexican border.

At least 23 people died on Friday after some 2,000 migrants stormed the heavily fortified border between the Moroccan region of Nador and the Spanish enclave of Melilla.

The African Union Commission has called for an investigation, voicing shock at the "violent and degrading" treatment of African migrants trying to cross into Spain.

Spain's enclaves in Morocco, Melilla and Ceuta, are the only land borders the European Union shares with Africa.