diff --git a/flang/lib/Lower/OpenMP.cpp b/flang/lib/Lower/OpenMP.cpp
--- a/flang/lib/Lower/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP.cpp
@@ -15,6 +15,7 @@
 #include "flang/Lower/FIRBuilder.h"
 #include "flang/Lower/PFTBuilder.h"
 #include "flang/Parser/parse-tree.h"
+#include "flang/Semantics/tools.h"
 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
 #include "llvm/Frontend/OpenMP/OMPConstants.h"
 
@@ -87,19 +88,34 @@
     auto &firOpBuilder = absConv.getFirOpBuilder();
     auto currentLocation = absConv.getCurrentLocation();
     auto insertPt = firOpBuilder.saveInsertionPoint();
+
+    // Clauses.
+    // FIXME: Add support for other clauses.
+    mlir::Value numThreads;
+
+    const auto &parallelOpClauseList =
+        std::get<Fortran::parser::OmpClauseList>(blockDirective.t);
+    for (const auto &clause : parallelOpClauseList.v) {
+      if (const auto &numThreadsClause =
+              std::get_if<Fortran::parser::OmpClause::NumThreads>(&clause.u)) {
+        // OMPIRBuilder expects `NUM_THREAD` clause as a `Value`.
+        numThreads = absConv.genExprValue(
+            *Fortran::semantics::GetExpr(numThreadsClause->v));
+      }
+    }
     llvm::ArrayRef<mlir::Type> argTy;
-    mlir::ValueRange range;
-    llvm::SmallVector<int32_t, 6> operandSegmentSizes(6 /*Size=*/,
-                                                      0 /*Value=*/);
-    // create and insert the operation.
+    Attribute defaultValue, procBindValue;
+    // Create and insert the operation.
+    // Create the Op with empty ranges for clauses that are yet to be lowered.
     auto parallelOp = firOpBuilder.create<mlir::omp::ParallelOp>(
-        currentLocation, argTy, range);
-    parallelOp.setAttr(mlir::omp::ParallelOp::getOperandSegmentSizeAttr(),
-                       firOpBuilder.getI32VectorAttr(operandSegmentSizes));
-    parallelOp.getRegion().push_back(new Block{});
+        currentLocation, argTy, Value(), numThreads,
+        defaultValue.dyn_cast_or_null<StringAttr>(), ValueRange(), ValueRange(),
+        ValueRange(), ValueRange(),
+        procBindValue.dyn_cast_or_null<StringAttr>());
+    firOpBuilder.createBlock(&parallelOp.getRegion());
     auto &block = parallelOp.getRegion().back();
     firOpBuilder.setInsertionPointToStart(&block);
-    // ensure the block is well-formed.
+    // Ensure the block is well-formed.
     firOpBuilder.create<mlir::omp::TerminatorOp>(currentLocation);
     firOpBuilder.restoreInsertionPoint(insertPt);
   }
diff --git a/flang/unittests/Lower/OpenMPLoweringTest.cpp b/flang/unittests/Lower/OpenMPLoweringTest.cpp
--- a/flang/unittests/Lower/OpenMPLoweringTest.cpp
+++ b/flang/unittests/Lower/OpenMPLoweringTest.cpp
@@ -8,6 +8,7 @@
 
 #include "gtest/gtest.h"
 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
+#include "mlir/IR/Attributes.h"
 #include "mlir/IR/Builders.h"
 #include "mlir/InitAllDialects.h"
 #include "flang/Parser/parse-tree.h"
@@ -16,6 +17,7 @@
 class OpenMPLoweringTest : public testing::Test {
 protected:
   void SetUp() override {
+    ctx.loadDialect<mlir::StandardOpsDialect>();
     ctx.loadDialect<mlir::omp::OpenMPDialect>();
     mlir::registerAllDialects(ctx.getDialectRegistry());
     mlirOpBuilder.reset(new mlir::OpBuilder(&ctx));
@@ -81,22 +83,31 @@
   // OpenMPDialect.
   EXPECT_EQ(parallelDirective.v, llvm::omp::Directive::OMPD_parallel);
   auto insertPt = mlirOpBuilder->saveInsertionPoint();
+  mlir::Value numThreads;
+  mlir::Attribute defaultValue, procBindValue;
+
+  // Construct a dummy value for `NUM_THREAD` clause.
+  numThreads = mlirOpBuilder->create<mlir::ConstantOp>(
+      mlirOpBuilder->getUnknownLoc(), mlirOpBuilder->getIntegerType(32),
+      mlirOpBuilder->getIntegerAttr(mlirOpBuilder->getIntegerType(32), 4));
+
   llvm::ArrayRef<mlir::Type> argTy;
-  mlir::ValueRange range;
-  llvm::SmallVector<int32_t, 6> operandSegmentSizes(6 /*Size=*/, 0 /*Value=*/);
-  // create and insert the operation.
+  // Create and insert the operation.
   auto parallelOp = mlirOpBuilder->create<mlir::omp::ParallelOp>(
-      mlirOpBuilder->getUnknownLoc(), argTy, range);
-  parallelOp.setAttr(mlir::omp::ParallelOp::getOperandSegmentSizeAttr(),
-      mlirOpBuilder->getI32VectorAttr(operandSegmentSizes));
+      mlirOpBuilder->getUnknownLoc(), argTy, mlir::Value(), numThreads,
+      defaultValue.dyn_cast_or_null<mlir::StringAttr>(), mlir::ValueRange(),
+      mlir::ValueRange(), mlir::ValueRange(), mlir::ValueRange(),
+      procBindValue.dyn_cast_or_null<mlir::StringAttr>());
   parallelOp.getRegion().push_back(new mlir::Block{});
   auto &block = parallelOp.getRegion().back();
   mlirOpBuilder->setInsertionPointToStart(&block);
-  // ensure the block is well-formed.
+  // Ensure the block is well-formed.
   mlirOpBuilder->create<mlir::omp::TerminatorOp>(
       mlirOpBuilder->getUnknownLoc());
   mlirOpBuilder->restoreInsertionPoint(insertPt);
+
   EXPECT_EQ(succeeded(parallelOp.verify()), true);
+  EXPECT_EQ(parallelOp.num_threads_var(), numThreads);
 }
 
 // main() from gtest_main