The head of the U.S. agency charged with overseeing cargo security met with officials in Sanaa to discuss the issue following last week's seizure of U.S.-bound package bombs sent from Yemen.

John Pistole, head of the U.S. Transportation Security Administration, met with Yemeni Deputy Prime Minister Rashad al-Alimi and aviation officials and he also toured a cargo facility in Sanaa, the agency said.

Investigators have been trying to determine whether the mail bombs, intercepted in Dubai and Britain after a tip from Saudi Arabia, were the work of the militant group al Qaeda in the Arabian Peninsula, or AQAP, which has previously tried to attack the United States.

"We face a determined enemy, one who modifies their actions looking for any opportunity to exploit security," Pistole said in a statement. "I am pleased with the work of our TSA inspectors and the cooperation of Yemeni officials to improve cargo security practices."

TSA, which is responsible for U.S. cargo and aviation security, has come under renewed scrutiny after the attempted mail bombs. Some U.S. lawmakers have called on the agency to improve screening of cargo.

The Department of Homeland Security, which includes TSA and the Customs and Border Protection Agency, boosted security after the discovery of the parcel bombs and halted cargo shipments from Yemen to the United States.

Homeland Security Secretary Janet Napolitano spoke with the chief executives at some of the leading global shipping companies, including United Parcel Service Inc, DHL and FedEx Corp, to discuss air cargo screening.

"Secretary Napolitano underscored her commitment to partnering with the shipping industry to strengthen cargo security through enhanced screening and preventative measures, including terrorism awareness training for personnel," Department of Homeland Security said in a statement.

Cargo shipped on planes to the United States must meet certain security requirements, including for screening, vetting of personnel in the facilities and providing advance manifests to authorities. (Reuters)