BERLIN (Reuters) - Germany's foreign minister warned Russia on Wednesday against increased military intervention in Syria, saying the Iran nuclear deal and new U.N. initiatives offered a starting point for a political solution to the Syrian conflict.

Frank-Walter Steinmeier made his comments after Russia, which along with Iran supports Syrian President Bashar al-Assad, said earlier on Wednesday it had military experts in Syria. Assad is opposed by most Western countries.

Germany is keen to negotiate an end to the more than four-year civil war in Syria, but France is considering launching air strikes against Islamic State militants there and Britain is ready carry out more.

"It can't be the case that important partners, who we need now, back the military option," Steinmeier told German lawmakers.

He expressed his dismay at reports that Russia is stepping up its provision of military equipment to Syria.

Sources close to Steinmeier said he was particularly dismayed at Russia's behavior and that his comments were aimed more at Moscow than at Paris or London.

Last week, Chancellor Angela Merkel said Germany would welcome Iran's participation in any negotiations aimed at ending the civil war in Syria.

Her comments reflected changing European attitudes towards Iran since it agreed in July to curb its nuclear work in exchange for sanctions relief.

With Germany holding the rotating presidency of the Group of Seven economic powers, Steinmeier said he would organize a meeting of G7 countries and Syria's Arab neighbors before the United Nations General Assembly later this month.

The meeting would aim to raise more funds for the U.N. refugee agency UNHCR.

(Reporting by Sabine Siebold, Writing by Paul Carrel; Editing by Alison Williams)