The United States joined Australia in warning tourists to avoid travel to part of eastern Malaysia, citing threats of kidnapping and piracy.
The U.S. warning highlights threats to tourists along the eastern coast of Malaysia's state of Sabah, where Islamic militants kidnapped 21 people five years ago.
The State Department said Saturday there are indications extremists in the region are planning a new series of attacks and urged Americans to avoid travel to the area.
Earlier this week, the Australian government said terrorists may be planning kidnapping attacks on resorts in Sabah that are popular with foreigners.
The Malaysian government strongly criticized the Australian warning and insists tourists in the region are well protected.
Local tour operators say the government has also beefed up security around Sabah's resorts and scuba diving centers.
Daniel Jemandan works for Absolute Scuba in Sabah. He says he sees no reason for tourists to cancel their plans and that, for now, business remains good.
"We don't see the effects so much," he said. "People are still coming. It's still safe because everything is under control."
But he says concerns remain about the long-term effects of the negative publicity.
The Malaysian government heavily promotes its tourist industry worldwide.
Nevertheless, concerns about a possible rise in Islamic extremism and terrorist threats could damage Malaysia's reputation with international travelers.
In 2000, militants from the Abu Sayyaf extremist group kidnapped 21 people, including 12 foreigners, from Sabah's Sipadan Island.
Abu Sayyaf is based in the southern Philippines and security experts believe it has strong ties with the al-Qaida-linked Jemaah Islamiyah terrorist network.