Bangladesh foreigner killings
Bangladeshi police officials stand guard at the site where a Japanese citizen was shot to death by attackers in Rangpur on October 3, 2015. A Japanese citizen was shot dead by gunmen in a northern Bangladesh town onOctober 3, police said, days after an Italian aid worker was murdered in an attack claimed by the Islamic State group. Police said the victim, whom they named as Hoshi Kunio, aged 66, was riding in a rickshaw when he was shot dead in Kaunia town in the Rangpur district at about 10:30 am local time. AFP/Getty Images

DHAKA (Reuters) - Bangladesh stepped up security for foreign diplomats and citizens on Sunday after the killing of two foreigners within a week in attacks claimed by Islamic State, which has vowed similar further assaults in the Muslim-majority nation.

Japanese citizen Kunio Hoshi, 65, was gunned down on Saturday by three masked men on a motorcycle while on his way to visit a grass farm project in the northern district of Rangpur, an attack similar to Tuesday's shooting of Italian aid worker Cesare Tavella.

Attacks on foreigners are rare in Bangladesh. But the country has been convulsed by a rising tide of Islamist violence over the past year in which four online critics of religious militancy were hacked to death, a U.S. citizen among them.

"Extra forces have been deployed at foreign diplomats and citizens' homes and workplaces across the country," Muntasirul Islam, a deputy commissioner of the Dhaka Metropolitan Police, told Reuters.

Police have not confirmed Islamic State, which has ambitions to spread into South Asia, is behind the two attacks. Dhaka police arrested two suspected recruiters for the hardline Islamist group over the past year.

On Saturday, Islamic State warned of more attacks.

"There will continue to be a series of ongoing security operations against nationals of crusader coalition countries, they will not have safety or a livelihood in Muslim lands," the group tweeted.

After Tavella's killing in the Gulshan neighborhood, home to several embassies, concerns that foreigners might be targeted prompted Western embassies to curtail the movements of diplomats in Bangladesh.

Australia postponed their tour of Bangladesh, saying on Thursday they were advised against going ahead with a two-test series that could expose their cricketers to potential militant attacks in the country.

Police are interrogating four people for clues to Hoshi's killing, but no arrests have been made over Tavella's murder.

The violence could pose a fresh threat to Bangladesh's $25-billion garment export industry, the economic lifeblood of the country of 160 million people.

Western buyers had begun to cancel visits after Tavella's shooting, said Shahidullah Azim, a garment exporter.

"One of my American buyers also canceled his Dhaka visit during peak time, when buyers are supposed to place more orders," he told Reuters.

"The killing of a Japanese citizen within a week has created more panic among foreign buyers."

The garment industry, which supplies Western brands such as Wal-Mart, JC Penney and H&M, has already been in the spotlight over several fatal accidents, such as the 2013 collapse of a building housing factories that killed more than 1,130 people.

(Reporting by Ruma Paul; Editing by Clarence Fernandez)