MOSCOW/UNITED NATIONS, April 29 -- Russia promised to help free detained European observers in eastern Ukraine on Monday as UN Secretary-General Ban Ki-moon strongly condemned the detention.

"We are doing some steps, not only by statements but also in practice," Russian envoy to the Organization for Security and Cooperation in Europe (OSCE) Andrey V. Kelin told reporters on Monday.

Russia has already worked to help release the OSCE military observers in the eastern Ukrainian town of Sloviansk, and some practical steps have been taken to ensure their release, said the envoy.

A German-led Vienna Document inspection team and their Ukrainian escorts were detained in Sloviansk on Friday by protesters. One Swedish inspector was released on Sunday, as he suffers diabetes.

Seven other inspectors and some Ukrainian military officers remained detained.

Ukrainian envoy to OSCE Ihor Prokopchuk later called on countries, particularly Russia, to work for the release of the other inspectors, their Ukrainian escorts and other hostages in Sloviansk.

Prokopchuk said his country was cooperating closely with OSCE for the release of the detainees.

Also on Monday, UN Secretary-General Ban Ki-moon urged "those responsible for their abduction to release them immediately, unconditionally and unharmed."

"The secretary-general strongly condemns the recent capture and detention of OSCE military monitors as well as a number of accompanying Ukrainian staff," said a statement issued by Ban's spokesman.

"He urges those responsible for their abduction to release them immediately, unconditionally and unharmed," said the statement.

"The secretary-general underlines that those who continue unlawful acts will be held accountable for their actions," the statement said.

Ban "appeals to all those with influence to assist in the urgent resolution of this matter," said the statement.

"The secretary-general stresses that international missions working in Ukraine must be allowed to perform their duties unimpeded," the statement said.

"The secretary-general urges all parties concerned to take immediate steps to de-escalate the situation in Ukraine," it said.

"He also calls on them to find a way back to the spirit of compromise exhibited during the Geneva talks on 17 April," the statement said, referring to an accord reached earlier this month by top diplomats from Ukraine, Russia, the United States and the European Union to de-escalate the situation in eastern Ukraine.

"A diplomatic and political solution to this crisis is imperative and long overdue," the statement said.

The observers, all Europeans, were part of a 12-member military verification team deployed last month by the Vienna-based OSCE in eastern Ukraine to monitor the political and security situation in the country following pro-Russia protests in its eastern region.

The team included seven military officers -- three from Germany and one each from the Czech Republic, Denmark, Poland and Sweden -- and a German interpreter, along with five members of the Ukrainian military as escorts.

The detainees were reportedly held in a basement for one day and then moved on Saturday to better quarters.