The US said it hoped that a high powered ministerial committee appointed to look into complaints of "harassment and death threats against media personnel" and intervene where needed.
"A press that is free of intimidation is an essential component of any democracy," the United States said.
"We call on the authorities to bring the perpetrators of this crime swiftly to justice," the United States embassy in Colombo said in a statement.
"We are deeply concerned by a series of recent incidents involving members of the Sri Lankan media."
UK embassy political officer Mahendra Ratnaweera and freelance journalist Namal Perera were clubbed and their car smashed by a group of unidentified men who blocked their vehicle in broad daylight Monday.
Sri Lanka's Free Media Movement (FMM), a rights body said Perera narrowly escaped being abducted in the same way Keith Noyahr, defence correspondent of The Nation newspaper was abducted and beaten recently.