ISTANBUL—U.S. Secretary of State Hillary Clinton discussed the Syrian crisis with her Turkish counterpart Ahmet Davutoglu in Istanbul on Saturday, amid a worsening conflict between regime and opposition forces inside Syria.

Mrs. Clinton´s visit was seen in Turkey as a reaffirmation of U.S. support for Turkey´s policy on Syria. Turkey has fiercely criticized the regime of President Bashar al-Assad and is hosting Syrian opposition groups, which are actively working to overthrow the regime, especially along the long border between the two countries.

Mrs. Clinton said in a joint press conference in Istanbul that the two countries´ foreign ministries were coordinating closely on Syria to support the opposition—in ways which said she did not want to describe in detail—as well as to aid democratic transition in Syria and end the humanitarian crisis caused by the conflict.

Mrs. Clinton said that the two allies are seeking to speed up the transition of power in Syria in a more concrete way.

"Our intelligence services, our military have very important responsibilities and roles to play, so we are going to be setting up a working group to do exactly that," she said.

Mrs. Clinton said that any use of chemical weapons, which the Syrian regime is known to possess, would be "the red line for the world."

"We have planned for many contingencies, including the very horrible scenario of the use of chemical weapons," she said.

The secretary of state also addressed Turkey´s fears over the grown influence and activities of the banned Kurdistan Workers´ Party, the PKK, in the predominantly Kurdish northeastern region of Syria. Turkey has fought the PKK since 1984 in a bloody war which had claimed some 40,000 lives.

"Syria must not become the haven for PKK terrorists," Mrs. Clinton said.

Before the meeting of Mrs. Clinton and Mr. Davutoglu, Mrs. Clinton also met Syrian opposition members in Istanbul.

"I was very impressed by these young activists," she said.

Mrs. Clinton is also scheduled to meet Prime Minister Recep Tayyip Erdogan and President Abdullah Gul.

Together with the latest influx of refugees to Turkey from Syria, the number of Syrians in Turkish camps has exceeded 55,000, according to Turkey´s foreign ministry figures. In recent days, a couple of thousand Syrians have crossed the border to Turkey on a daily basis. (Copyright © Dow Jones & Company, Inc.) 08/12/12)