* Medecins Sans Frontieres says seeing more tank, aircraft wounds
* Sign Assad forces using heavier weaponry after Damascus bombing
* Charity opens hospital in northern Syria
By John Irish
PARIS, Aug 21 (Reuters) - Medics in Syria have been treating more wounds from tank and aircraft bombardment in the past month, charity Medecins Sans Frontieres said on Tuesday, the latest sign government forces are using heavier weaponry to try to crush the uprising.
Wounds inflicted on victims of the violence have worsened since the July 18 rebel bomb attack that killed members of President Bashar al-Assad's inner circle, including his defence minister and brother-in-law, the medical organisation said.
Medics from the charity are seeing more injuries from tank shelling, aerial bombardment and heavy artillery than at any other time during the 17-month-old conflict which has killed 18,000, MSF said.
"We saw big changes after the bombing of the security forces in Damascus in July with the degradation of security," Brian Moller, an anaesthetist nurse who is heading up an MSF mission in northern Syria, told Reuters.
"This attack emboldened the Free Syrian Army and then we started seeing injuries from large ordnance shelling ... The injuries are graphic."
At least 170,000 people have fled the violence in Syria, according to the United Nations, and 2.5 million need aid inside the country.
Paris-based MSF, which until now had declined to detail its operations in Syria, said it had sent a team of medics to the north of Syria in June to open a hospital that has been working around the clock since.
The team has so far carried out about 150 operations at the site on women, children and men, including FSA fighters, with injuries ranging from sniper fire wounds to puncture wounds from heavy mortar rounds, which break into fragments upon impact.
The seven MSF medics in Syria include surgeons and anaesthetists and are backed up by about 50 local workers, MSF staff who returned to the organisation's Paris headquarters this week to be relieved by colleagues told reporters.
MSF General Manager Felipe Ribeiro told Reuters the charity had informed Syrian authorities about the hospital and had been "politely" told to leave the country. However, they had not received any direct threats and were in a safe zone under rebel control, he said.
With diplomatic efforts to end the war stymied by divisions between world powers and regional rivalries, Syria faces the prospect of a prolonged conflict that increasingly sets a mainly Sunni Muslim opposition against Assad's Alawite minority.
MSF has secretly been sending medics into Syria for short periods for almost a year and working with local groups. After failing to get government approval to set up a base, it said it opted to go it alone in an area where Assad's forces had least control.
The hospital has a maximum capacity of 30 patients and includes 12 beds, operating theatres and an ultrasound machine.
"We looked for a place where we could guarantee access for patients, security of our staff and continuity of care, so that's why we decided to take the risk to set up a 24/7 hospital inside Syria," Ribeiro said.
Victims mostly discover the hospital through word of mouth and some of those treated had travelled as far as 150 km (93 miles) to reach it, MSF said.
The hospital has supplies to last two weeks and while it is difficult to get them into the country, MSF's local network has so far allowed it to maintain operations.
(Reporting By John Irish; Editing by Pravin Char)