Iraqi forces have in recent days been massing around Fallujah, a city just 50 kilometres west of Baghdad and which has been out of government control since January 2014.
The attack on the gas plant started at dawn with a suicide car bomber hitting the facility’s main gate in the town of Taji, about 20 kilometers (12 miles) north of Baghdad.
He is the third American killed in direct combat since a US-led coalition launched a campaign against the jihadist group in 2014.
The group said in an online statement distributed by supporters that a suicide bomber had targeted pilgrims in the Dora neighbourhood adjacent to Saydiya.
“The hospitals have received 33 dead,” a senior official in the Muthanna health department, which covers Samawa, told AFP.
IS claimed the attack and said it was carried out by a suicide bomber who detonated a vehicle laden with three tonnes of explosives.
Iraq’s Communications and Media Commission (CMC) sent the Al-Jazeera Media Network a letter informing it of a March 24 decision to withdraw the bureau’s licence and close its office for one year.
The US President’s instructions to his national security team have been to reinforce the successful elements of US campaign
“Terrorism is an urgent global security threat that requires international collaboration and unified responses,” they said in a statement at the end of a two-day meeting in the Japanese city of Hiroshima.
The bombing took place on Friday during a match in the small stadium in the city of Iskanderiyah, 30 miles from Baghdad. IS claimed the attack, saying it had targeted Shiite militiamen.
Some US and Iraqi officials have said it may not even be possible to retake it this year, despite repeated vows by Iraqi Prime Minister Haider al-Abadi.
Khweis gave himself up to Iraqi Kurdish forces in northern Iraq on Monday. As IS loses territory, US officials predict there will be more desertions.
The Cessna 208 Caravan single-engine turboprop crashed on Wednesday while hovering near the town of Hawija, 130 miles north of Baghdad.
The attacker struck shortly after noon when the checkpoint at one of the entrances to the city of Hillah was crowded with dozens of cars, a police officer said.
The official said the group has spent the last several weeks preparing, including setting up safe houses, establishing informant networks and coordinating operations with Iraqi and Peshmerga units.