The Wall Street Journal reports: Officers at the Pentagon on Thursday were updating target lists for possible airstrikes on a range of Syrian government and military installations, officials said, as part of contingency planning should President Barack Obama decide to act after what experts said may be the worst chemical-weapons massacre in more than two decades.

As the Pentagon worked on its options, Secretary of State John Kerry talked by telephone with French Foreign Minister Laurent Fabius and the foreign-policy chiefs of Turkey, Jordan and the European Union, as well as with United Nations Secretary-General Ban Ki-moon, officials said.

The Syrian government denied allegations it gassed its own people, backed by new statements from regime allies Iran and Russia accusing Syrian President Bashar al-Assad’s international foes of conspiring against him. U.S. officials said they have seen “strong indications” that chemical weapons were used but that more work was needed to evaluate and collect evidence.

The regime gave no indication, however, that it would agree to Mr. Ban’s plea to let U.N. inspectors investigate the chemical-weapons allegations, as Syrian forces pressed on with an offensive in the towns around the capital where the attacks were alleged to have occurred.

U.S. officials who described the military options being revised at the Pentagon stressed that their purpose wouldn’t be to topple the regime, but to punish Mr. Assad if there is conclusive evidence that the government was behind poison-gas attacks on Wednesday.

Making its options known could constitute a U.S. warning to Mr. Assad and his backers. It was unclear if Mr. Obama would be prepared to use the options; he has resisted getting entangled militarily in the conflict since the start.