LONDON- Bahrain and Qatar's credit ratings are the most vulnerable in the event an escalation of U.S.-Iran tensions causes blockages in the Strait of Hormuz, one of the world's main oil shipping arteries, S&P Global said on Thursday.

Suspected attacks on two tankers off the coast of Iran saw oil markets erupt out of their recent slump on Thursday, with the incident adding to already-heightened tensions between Iran and Washington. 

"Bahrain appears to be the most vulnerable Gulf sovereign," to any blockages in the Strait of Hormuz, a strait between the Persian Gulf and the Gulf of Oman, S&P said in a new report, also citing Bahrain's weak fiscal position.

Qatar is also vulnerable, it added, because of its high external financing needs, at about 180% of current account receipts (CARs) plus usable reserves, largely due to the foreign funding of its banking system.

(Reporting by Marc Jones, Editing by Helen Reid) ((marc.jones@thomsonreuters.com; +44 (0)207 542 9033; Reuters Messaging: marc.jones.thomsonreuters.com@reuters.net Twitter @marcjonesrtrs))