"We have heard that embassies are experiencing cash flow problems due to the impact on sanctions on money transfers, which we hope will get sorted out. Without this process through the US Embassy, we will be unable to continue to pay for Paul's phone calls home, the Whelan family said in a statement.
Paul's morale remains high, but that may change as the situation develops, the statement also said.
"Already, the United States Postal Service has suspended mail delivery to Russia. The loss of phone calls would sever any ability for Paul to communicate beyond the walls of his hostage takers," the statement added.