South Korea fires warning shots at North Korea after an 'unidentified object' flies over DMZ

South Korea has fired into North Korea after an "unidentified object" was sent towards the country.

South Korea's Joint Chiefs of Staff said in a statement that the South Korean military bolstered its air surveillance and broadcast a warning to North Korea in response to the object. It provided no other details.

The mystery flying object may have been a drone, local media speculated.

South Korea's Yonhap news agency, without citing a source, reported that South Korea fired about 90 machine gun rounds into the air and toward North Korea. It said South Korea was analyzing whether a North Korean drone had crossed the border.

In 2014, South Korean officials discovered what they described as several North Korean drones that had flown across the border. Those drones were crude and low-tech, but were still considered a potential new security threat.

The Koreas face off across the world's most heavily armed border, and the two sides occasionally clash. In 2014, they traded machine gun and rifle fire after South Korean activists released anti-North Korean propaganda balloons across the Demilitarized Zone that bisects the Korean Peninsula, but no casualties were reported.

Attacks blamed on North Korea in 2010 killed 50 South Koreans.

The United States has been trying to persuade China, North Korea's lone major ally, to do more to rein in North Korea, which has conducted dozens of missile launches and tested two nuclear bombs since the start of last year, in defiance of U.N. Security Council sanctions and resolutions.

The North has made no secret of its plans to develop a missile capable of striking the United States and has ignored calls to halt its weapons programmes, even from China. It says the programme is necessary to counter U.S. aggression.

"We urge North Korea to not do anything to again violate U.N. Security Council resolutions," Chinese Foreign Minister Wang Yi said in a statement posted on the Foreign Ministry's website on Tuesday.

"At the same time, we hope all parties can maintain restraint, not be influenced by every single incident, ...persist in carrying out Security Council resolutions on North Korea and persevere with the resolution of the issue through peaceful means, dialogue and consultation."

Wang was responding to reporters' questions on Monday while in Ivory Coast, according to the statement.

The North's official KCNA news agency, citing the spokesman for the foreign ministry, said the country had "substantially displayed" the capabilities for mounting a nuclear attack on Hawaii and Alaska and had built full capabilities for attacking the U.S. mainland.

U.S. and South Korean officials and experts believe the North is several years away from having such a capability.

North Korea said on Monday that Sunday's launch met all technical requirements that could allow mass-production of the missile, which it calls the Pukguksong-2.

The test was North Korea's second in a week and South Korea's new liberal government said it dashed its hopes for peace on the peninsula.

The U.N. Security Council condemned the launch and again expressed its concern over the North's behaviour. The Security Council is due to meet behind closed doors later on Tuesday.

North Korea's recent missile tests were a legitimate act of self-defence by a "fully-fledged nuclear power", North Korean diplomat Ju Yong Chol told the U.N. Conference on Disarmament in Geneva on Tuesday.

"It is the United States' hostile policy and its aggressive joint military drills, nuclear threats and military build-up around the Korean peninsula that really aggravates the situation on the Korean peninsula and the region and which compels the DPRK to also up its nuclear deterrence," he said.

DPRK are the initials for the North's official name, the Democratic People's Republic of Korea. Ju was the only speaker at the forum who did not begin his remarks by offering condolences to Britain for the victims of Monday night's bomb attack at a concert in Manchester.

The South Korean military did not say if the unidentified object was hit by the warning shots on Tuesday, but it disappeared from military radar.

North Korea has previously sent drones into South Korean airspace, with some crashing. In January 2016, South Koreafired warning shots at a suspected drone which turned back.

U.S. President Donald Trump has warned that a "major, major conflict" with North Korea is possible over its weapons programmes, although U.S. officials say tougher sanctions, not military force, are the preferred option to counter the North Korean threat.

Additional reporting by agencies