UNITED NATIONS - UN Secretary-general Ban Ki-moon has asked the head of the UN fact-finding mission on the alleged use of chemical weapons in Syria, Ake Sellstrom, to visit New York for consultations on Monday, a UN spokesman told reporters here on Friday.

"The United Nations remains in close contact with the Syrian authorities, most recently through another letter from Angela Kane, the High Representative for Disarmament Affairs, on Thursday, urging the Syrian government to grant access without conditions to the mission," said Martin Nesirky, Ban's spokesperson, at a daily briefing.

"The secretary-general strongly urges the Syrian government to respond swiftly and favorably so that this mission can carry out its work in Syria," Nesirky said.

On March 26, Ban announced the appointment of Professor Ake Sellstrom of Sweden to head the UN fact-finding mission, which is tasked to investigate the alleged use of chemical weapons in Syria.

The Syrian government has recently asked the United Nations to send a technical team to the northern town of Khan al-Asal to investigate what it said was a chemical attack by the rebels, which killed more than 50 people and sent scores of others into hospitals. But the government also stressed that the technical team should conduct its work only at the targeted site.

However, Syrian opposition groups in exile have called on the United Nations not only to send a technical team, but also to conduct a full investigation.

On April 8, the Syrian Foreign Ministry said that the UN request to conduct a full investigation about chemical weapons on all Syrian territories runs counter to the request of the Syrian government.

At the Friday briefing, the UN spokesperson said that the team has already been doing work outside of Syria and has been gathering and collating evidence.

However, there is a need for the team to be able to have access to the country, Nesirky stressed. "In the meantime, the team will continue with off-site activities that may include the visits to capitals," he added.