When asked by [Christian Post] about the [Orange County] Register’s lead paragraph that states he “has embarked on an effort to heal divisions between evangelical Christians and Muslims by partnering with Southern California mosques and proposing a set of theological principles that includes acknowledging that Christians and Muslims worship the same God,” Warren stated:
”First, as I’ve already said, Christians have a fundamentally different view of God than Muslims. We worship Jesus as God. Muslims don’t. Second, while we urge members to build friendships with Muslims and everyone in our community (“Love your neighbor as yourself”), our church has no partnership with any mosque. For example, I know that some of our members have led Bible study with Muslim friends, which I applaud. But I’ve never been to it, and it certainly isn’t any kind of partnership or merger. It’s crazy how a simple Bible study can be interpreted by some people as a plan for a new religion!”

The primary talking point of the controversy appears to be the question as whether Christians and Muslims worship the same God.

Warren’s answer: 
”Of course not. Christians have a view of God that is unique. We believe Jesus is God! We believe God is a Trinity: Father, Son, and Holy Spirit. Not three separate gods but one God. No other faith believes Jesus is God. My God is Jesus. The belief in God as a Trinity is the foundational difference between Christians and everyone else. There are 2.1 billion people who call themselves Christians… whether Catholic, Orthodox, Protestant, Pentecostal, or Evangelical… and they all have the doctrine of the Trinity in common.” (Online source)

See also:

RICK WARREN, ISLAM, AND JIM HINCH

JOHN PIPER, RICK WARREN & FOSTER-WILLARDISM

JAMES ROBISON AND RICK WARREN WORKING TO REVERSE THE PROTESTANT REFORMATION