The UN Security Council has expanded targeted sanctions against North Korea in response to a series of missile tests conducted by Pyongyang this year, BBC News reports.

The measures impose a travel ban and asset freeze on four entities and 14 officials, including the head of North Korea's overseas spying operations.

The council voted unanimously to back the sanctions after weeks of negotiations between the US and China.

Pyongyang has defied a UN resolution banning all nuclear and missile tests.

The sanctions resolution was adopted by the 15-member council on Friday.

Among the 14 North Korean officials is Cho Il-u, who leads Pyongyang's foreign espionage operations.

The other blacklisted officials are senior members of North Korea's Workers' Party and heads of trading firms funding Pyongyang's military programme.

North Korea's strategic rocket force, the Koryo Bank and two trading firms were also added to the list.

The Koryo Bank is linked to a party office that manages finances of North Korea's top officials, including leader Kim Jong-un.

Pyongyang has been testing its missiles at an unprecedented pace. It says its nuclear programme is defensive and intended to counter US aggression.

But experts fear the tests indicate progress towards Pyongyang's ultimate goal of putting a nuclear warhead on a missile that could strike the continental US.

US President Donald Trump has warned North Korea that America's "strategic patience" over the North's nuclear ambitions came to an end.

Washington has recently sent its aircraft carrier to the Korean peninsula.

At the same time, the US has been negotiating with China - North Korea's ally - to put more pressure on the secretive regime.

The UN Security Council first imposed sanctions against North Korea in 2006 in response to its missile and nuclear programmes.

The council has since strengthened its measures.