The US on Thursday issued guidance easing the way for delivery of goods such as face masks, ventilators and vaccines to battle the pandemic in Iran, Venezuela and Syria, on which it has heavily imposed sanctions.
The US Treasury Department issued general licences to allow more coronavirus-related transactions and activities, it said, but did not lift any sanctions.
The move comes after US President Joe Biden, on his first full day in office in January, issued a national security memo calling for his administration to review sanctions and evaluate whether they were hindering responses to the pandemic.
"Even though we have comprehensive humanitarian general licences in all our programmes, we did see some gaps," a US Treasury official said.
The official said that before Thursday's move, obstacles were dealt with on a case-by-case basis that involved delay and cost.
"This is lowering that barrier."
The administration of president Donald Trump had been criticised by human rights groups for not softening sanctions rules against countries such as Iran and Venezuela to ease pandemic-related hardship.
The new Venezuela licence authorises pandemic-related deals involving the Venezuelan government and some of its banks.
Top Venezuelan officials and the financial sector have been subject to heavy sanctions imposed in the Trump era to remove socialist President Nicolas Maduro.
Venezuelan officials said last week they could not complete a $10 million payment to the global Covax vaccine programme because bank transfers for part of the funds had been blocked.
Caracas has repeatedly blamed US "blockade" for its slow distribution, although critics say Mr Maduro's government has undermined talks with the opposition to secure vaccines.
In the new Iran general licence, the Treasury Department is authorising “all transactions and activities related to the exportation, re-exportation, sale or supply, directly or indirectly, of goods or technology for use in connection with the prevention, diagnosis or treatment of Covid-19".
It allows transactions that have until now been prohibited by sanctions on Iran’s central bank and national oil company related to the fight against the coronavirus.
"[Treasury's Office of Foreign Assets Control] encourages those interested in providing Covid-19-related relief to Iran, Syria and Venezuela to avail themselves of the available exemptions, exceptions and authorisations pertaining to humanitarian assistance," Treasury said.