UNITED NATIONS, May 2 (Xinhua) -- UN Secretary-General Ban Ki- moon on Friday reiterated his "grave concern" over the deteriorating situation in regions of east and south Ukraine, stressing that a "diplomatic solution is the only way out of this crisis."
Ban made the remarks in a statement issued here by his spokesperson after Ukraine launched a military operation on Friday against the eastern city of Slaviansk, which had been reportedly seized by pro-Russia forces.
"Escalating violence and reported further loss of life in the city ... is a stark reminder of how dangerous the situation has become," he said in the statement. "Expansion of militia activities and ongoing seizures of public buildings by unidentified armed groups undercut the letter and spirit of the April 17 Geneva statement."
While calling for full respect to Ukraine's sovereignty and territorial integrity, Ban urged "all sides to exercise maximum restraint and appealed to those with grievances to voice them peacefully, so as to avoid more bloodshed."
Ban noted that a diplomatic solution is the only way out of this crisis and that all sides must redouble their efforts to revive the spirit of compromise displayed during the 17 April Geneva talks, said the statement.
The UN chief also called on those responsible for the capture and detention of OSCE (Organization for Security and Cooperation in Europe) military monitors and accompanying Ukrainian staff to release them "immediately, unconditionally and unharmed," said the statement.
Ban has asked UN Under-Secretary-General for Political Affairs Jeffrey Feltman to travel to Moscow and Kiev next week to meet with senior officials and international partners to promote de- escalation and work toward a peaceful resolution of the crisis in Ukraine.
Feltman will be carrying a strong message from the secretary- general that all actors need to exercise utmost caution to prevent the extremely fragile situation from spinning out of control and stress the need for a return to diplomacy and highlight the willingness of the United Nations to play a good offices role, said the statement.
Ukraine launched a major attack against pro-Russia forces around the city of Slaviansk in the early hours of Friday. Rebels shot down two Ukrainian helicopters and killed one crew member, according to Vyacheslav Ponomaryov, leader of Slaviansk's self- defense forces.
Ponomaryov accused the Ukrainian authorities of launching the attack using heavy weapons, saying the self-defense forces had to withdraw into the city.
Ukrainian defense ministry confirmed the loss of the two helicopters, but said two crew members were killed.
It added that the helicopters were shot down with a surface-to- air missile, which proved the rebels were not civilians but well- equipped and well-trained military.
Ukraine Interior Minister Arsen Avakov warned Slaviansk residents to remain indoors while anti-terrorism operations proceeded in the city.