WASHINGTON (AFP) - The United States said on Tuesday it will boost security at government buildings following threats from Islamist groups.

The "precise actions" and "precise locations" were not specified in the statement by Secretary of Homeland Security Jeh Johnson, who said they would vary, shift and "be continually reevaluated". "The reasons for this action are self-evident," Mr Johnson said, citing "continued public calls by terrorist organisations for attacks on the homeland and elsewhere" as well as the two attacks last week in Canada and elsewhere.

Mr Johnson called it "a precautionary step, to safeguard US government personnel and facilities, and the visitors to those facilities" in the capital and other major cities, as well as other locations around the country.

The Federal Protective Service oversees security at more than 9,500 federal facilities, Mr Johnson said, which see some 1.4 million visitors and occupants daily.

On Thursday, in an attack branded a "terrorist act" by the police, a self-radicalised Muslim convert charged officers with a hatchet in a busy shopping area of New York City, striking two before he was shot dead by the two other officers, who were uninjured.

The attacker Zale Thompson, 32, appeared to have acted alone and was not affiliated to a particular group, but the police said he had looked at websites about groups such as Al-Qaeda and Islamic State in Iraq and Syria (ISIS).

Earlier last week, two attacks in Canada killed two soldiers. In one, a soldier was fatally shot while standing watch at the War Memorial in Ottawa.

His attacker, Michael Zehaf-Bibeau, then stormed into Parliament and exchanged fire with police before being shot dead himself.

In the other, 25-year-old Martin Couture-Rouleau, who had been on a watch list of suspected extremists, used his car as a weapon to run over two soldiers in a parking lot, killing one of them before being shot dead by police.

Both assailants were converts to Islam with alleged extremist views, the police have said.

The two attacks in Canada came as it deployed fighter jets to join US-led air strikes on ISIS.

Canada is a member of the alliance Washington has forged of Western and Arab nations to combat ISIS, which seized large parts of Syria and Iraq in recent months, declaring an Islamic "caliphate" and committing widespread atrocities.

The group has called for foreign fighters to join them and promoted attacks by disaffected Muslims on Western targets.

"Given world events, prudence dictates a heightened vigilance in the protection of US government installations and our personnel," Mr Johnson said.