* Assad only wants U.N. team to investigate Aleppo incident
* U.N. investigator Sellstrom in Washington for talks
* U.N. urges Syria to grant Sellstrom's team broad access
The government of Syrian President Bashar al-Assad on Monday invited chief U.N. chemical weapons investigator Ake Sellstrom to Damascus to discuss allegations of banned arms use in Syria's civil war but suggested it would not compromise on access.
Syrian U.N. Ambassador Bashar Ja'afari told reporters that U.N. disarmament chief Angela Kane was also invited to Syria for talks about the U.N. chemical investigation.
So far Sellstrom's team has not been active on Syrian territory because Assad's government is only willing to allow it access to the city of Aleppo, where both sides have accused the other of using chemical weapons.
"We are sure that Ms Kane and Dr Sellstrom will have constructive negotiations with the Syrian officials in order to reach an agreement, a mutual agreement on the terms of reference, mechanism and time frame of the mission," he said.
Ja'afari said if they accept, the U.N. officials will be meeting with the Syrian foreign minister and national experts.
The Syrian envoy also made a fresh allegation against the rebels, suggesting they were stockpiling toxic chemicals.
"The Syrian authorities have discovered yesterday in the city of Banias 281 barrels filled with dangerous, hazardous chemical materials," he said, adding that the chemicals were "capable of destroying a whole city, if not the whole country."
Ja'afari said an investigation of the chemicals - which included monoethylene glycol and polyethylene glycol and were found at a storage site he said was linked to the "armed terrorist groups" - was still underway.
The Syrian government has denied using chemical weapons. It has in turn accused rebels of deploying them in the two-year civil war that the United Nations says has killed over 90,000 people since March 2011. The rebels deny responsibility for any chemical attacks.
U.N. Secretary-General Ban Ki-moon has urged Syria to give Sellstrom unfettered access to investigate all alleged chemical arms incidents. But Assad's government only wants the U.N. team to probe an incident in Aleppo from March, not others the U.S., Britain and France have written to Ban about. U.N. officials say U.N.-Syria negotiations on access have reached a deadlock.
Ja'afari was asked if the invitation to Sellstrom and Kane meant that Syria would consider allowing the U.N. team to go beyond Aleppo. He indicated that his government would not permit that, saying: "No, you wouldn't jump to this conclusion."
WRANGLING OVER ACCESS
Ban's spokesman Martin Nesirky did not say whether the U.N. investigators would accept the invitation, which he described as "a move in the right direction." He said the Syrian government needed to grant Sellstrom's team broad access across Syria "without further delay and without conditions."
Sellstrom's team has been ready for well over two months to enter Syria but has been held up by the wrangling over access.
They recently visited neighboring to try to gather information. Acting U.S. Ambassador to the United Nations Rosemary DiCarlo told reporters Sellstrom was in Washington on Monday for discussions with U.S. officials.
Ja'afari repeated Syria's allegation that accusations of chemical attacks by government forces were an attempt to undermine their initial request for a U.N. investigation focusing solely on the Aleppo incident from March.
One senior Western diplomat said last month that Britain and the United States alone have notified Ban of 10 separate incidents of the use of chemical weapons by Assad's forces. France has also said its own tests of samples from inside Syria proved Assad's forces have used the nerve agent sarin.
Sellstrom is expected to deliver an interim report this month. U.N. envoys say it may just be oral and will likely be inconclusive since it is impossible for him to make definite pronouncements about the chain of custody of the samples he has received from Britain, France and the United States.
Syria is one of seven countries that has not joined the 1997 convention banning chemical weapons. Western nations believe it has caches of undeclared mustard gas, sarin and VX nerve agents.